AU2016266463B2

AU2016266463B2 - Method for comprehensive recovery of smelting wastewater containing magnesium

Info

Publication number: AU2016266463B2
Application number: AU2016266463A
Authority: AU
Inventors: Zongyu FENG; Xiaowei Huang; Xinlin Peng; Xu SUN; Liangshi Wang; Meng Wang; Chao XIA; Yang Xu; Na Zhao
Original assignee: Grirem Advanced Materials Co Ltd
Current assignee: Grirem Advanced Materials Co Ltd
Priority date: 2015-05-26
Filing date: 2016-05-23
Publication date: 2019-07-18
Anticipated expiration: 2036-05-23
Also published as: CN106277417A; KR102093004B1; WO2016188387A1; KR20170138561A; AU2016266463A1

Abstract

A method for comprehensive recovery of smelting wastewater containing magnesium comprises: adjusting a pH value of acid smelting wastewater containing magnesium sulfate by using an alkaline substance, so as to obtain slurry containing magnesium hydroxide and calcium sulfate, the alkaline substance being an alkaline substance containing calcium; and introducing carbon dioxide gas into the slurry to perform carbonization, and then performing solid-liquid separation to obtain solid slag and magnesium bicarbonate solution. By means of key procedures such as neutralization, precipitation, carbonization and purification, calcium ions are converted into calcium sulfate and a small amount of calcium carbonate that is to be precipitated and recycled for use, and the content of calcium sulfate in the recycled water is reduced, thereby effectively solving the problem of scaling of pipelines, conveying pumps and storage tanks; magnesium ions in the smelting wastewater containing magnesium are converted into a magnesium bicarbonate solution that can be returned for smelting separation, and accordingly, the cyclic utilization of materials in the production process is implemented, and zero emission of wastewater is achieved.

Description

A METHOD FOR COMPREHENSIVE RECOVERY OF SMELTING WASTEWATER CONTAINING MAGNESIUM Technical field

The present invention relates to the field of smelting separation, and in particular to a method for comprehensive recovery of smelting wastewater containing magnesium.

Background art

In the production process of wet smelting separation, a large amount of wastewater has been produced. For example, Baotou mixed rare earth ore mainly uses sulfuric acid calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation separation process, and the wastewater produced in this process is mainly acidic wastewater produced during extraction and transformation of rare earth solution of sulfuric acid. The main components in the wastewater are sulfuric acid, hydrochloric acid, Mg ion, Ca ion, Al ion, F ion and heavy metal ions (such as Pb, Cd and As), and the like.

In the wastewater treatment process of the wet smelter, in order to neutralize a large number of acidic wastewater, the neutralization treatment in the traditional chemical neutralization method is conducted by adding lime or carbide slag and the like, resulting in a large number of precipitates such as calcium sulfate, calcium fluoride, magnesium hydroxide, etc.. After being clarified, the wastewater is discharged up to standard. Although the treatment process mainly consumes lime, carbide slag and other neutralizer, but the precipitation amount is large, the precipitates are complex and the operating environment is bad, the most important is that the recycling of the treated wastewater is limited. So in the wastewater treated by this process, the contents of calcium, magnesium and sulfate are saturated. In recycling, it will form calcium sulfate scale in the pipelines, conveying pumps and storage tanks and other devices with the change of temperature, and thus have a greater impact on the continuous production. In addition, the wastewater treated by this process has a very high salt content, and direct discharge will lead to an increase in the salinity of the river, causing serious pollution to the soil, surface water and groundwater, leading to further deterioration of the ecological environment. With the implementation of the new environmental law, it will be the ultimate goal to solve the problem of high salt wastewater and make the wastewater near zero discharge.

In the research and application of the recycle treatment of smelting wastewater, the current research is more of the use of membrane separation method, evaporation crystallization method, steam stripping method and broken point chlorination method and the like. The membrane separation method is the use of selective separation to separate ions, molecules or particles in water; the treatment effect is better, but it is easy to cause membrane contamination. The evaporation crystallization method is that the salt-containing wastewater is concentrated by evaporation to reach the supersaturated state, so that the salts in the wastewater form nuclei, and then gradually generate crystalline solid and then achieve separation. This method is suitable for the treatment of high salt wastewater. The steam tripping is that makes the wastewater and water steam in direct contact to diffuse the volatile substances in the wastewater to the gas phase in a certain proportion, so as to achieve the

2016266463 21 Jun 2019 purpose to separate pollutants from the wastewater, mainly being used for the handling of volatile pollutants. The break point chlorination method is that a certain amount of chlorine gas or sodium hypochlorite is added to the wastewater, so that ammonia nitrogen is oxidized to N₂, so as to 5 achieve the purpose of removing ammonia nitrogen. These methods have the disadvantages of high operating costs and large investment costs, so the application in the industry has been limited.

Therefore, in terms of the comprehensive utilization of smelting wastewater, there is still a need to improve the existing technique to io provide a treatment process for wastewater which is inexpensive, environmentally friendly and the wastewater after being treated can be recycled.

Summary of the present invention

The present invention desirably provides a method for comprehensive recovery of smelting wastewater containing magnesium, so as to provide a treatment process for wastewater which is inexpensive, environmentally friendly and the treated wastewater can be recycled.

According to one aspect of the present invention, there is provided a 20 method for comprehensive recovery of smelting wastewater containing magnesium, the method comprising the steps of: step SI, comprising steps Sil, S12 and SI3; step Sil, adjusting the pH of the smelting wastewater containing magnesium to 4.0 to 10.0 with a basic substance containing calcium to obtain a solid-liquid mixture, wherein the smelting 25 wastewater containing magnesium is acidic wastewater containing magnesium sulfate; step S12, filtering the solid-liquid mixture to obtain a

2016266463 21 Jun 2019 filtrate; and step S13, adjusting the pH of the filtrate to 10.0 to 12.5 with the basic substance containing calcium to obtain a slurry containing magnesium hydroxide and calcium sulfate; and step S2, introducing carbon dioxide gas into the slurry containing magnesium hydroxide and 5 calcium sulfate to perform carbonization, and performing solid-liquid separation to the carbonized slurry to obtain a solid slag and a magnesium bicarbonate solution.

Preferably, the smelting wastewater containing magnesium is wastewater containing magnesium sulfate produced by sulfation 10 calcination, water leaching, magnesium oxide neutralization and impurity removal and extraction-transformation process during smelting separation.

Preferably, the step Sil further comprises the step of adding a calcium sulfate seed crystal to the smelting wastewater containing 15 magnesium; and/or the step of subjecting the slurry containing magnesium hydroxide and calcium sulfate to an aging treatment.

Preferably, in the step of subjecting the slurry containing magnesium hydroxide and calcium sulfate to an aging treatment, the aging time is 0.5 h to 6 h.

Preferably, the step S2 comprises the steps of: introducing carbon dioxide gas into the slurry containing magnesium hydroxide and calcium sulfate to perform carbonization and controlling the pH of the slurry in the range of 6.5 to 8.0 during the carbonization to obtain a carbonized slurry; and performing solid-liquid separation to the carbonized slurry to obtain the solid slag and the magnesium bicarbonate solution.

2016266463 21 Jun 2019

Preferably, the calcium ion concentration in the magnesium bicarbonate solution is 0.01 g/L to 0.7 g/L, preferably 0.01 g/L to 0.4 g/L.

In certain embodiments, the solid slag is subjected to purifying treatment to produce calcium sulphate or is returned to neutralize the 5 acidic wastewater produced by smelting separation to produce calcium sulphate.

Preferably, the carbon dioxide gas is produced from a process exhaust gas comprising one or more of boiler flue gas, calcined kiln gas of oxalate precipitation and carbonate precipitation and the gas produced io by saponification extraction of the magnesium bicarbonate solution.

Preferably, in the step S2, the magnesium bicarbonate solution is used in a wet smelting procedure, wherein the smelting procedure is one or more of ore sulfating calcining-water leaching-neutralization and impurity removal procedure, acid leaching-neutralization and impurity 15 removal procedure, solution extraction and transformation or precipitation transformation procedure, solution extraction-separation procedure and solution precipitation procedure.

In an aspect, the present invention adjusts the pH to 10.0 to 12.5 by adding a basic substance to the smelting wastewater containing 20 magnesium. A large amount of Ca is converted into calcium sulfate precipitate while the Mg in the wastewater is converted into magnesium hydroxide, and after carbonization treatment, magnesium hydroxide is converted into soluble magnesium bicarbonate, and a small amount of calcium ions is further removed in the form of calcium carbonate 25 precipitate to achieve a relatively thorough separation of calcium ion and magnesium ion, so that the calcium ion concentration in the aqueous

2016266463 21 Jun 2019 solution of magnesium bicarbonate being recycled is low, which may desirably alleviate the problem of scaling of pipelines, conveying pumps, storage tanks and the like when water is recycled.

Brief description of the drawings

The drawings of the description, which constitute a part of this application, are intended to provide a further understanding of the present invention, and illustrative embodiments of the present invention and its description are intended to explain the present invention and do not 10 constitute an undue limitation to the present invention. In the drawings:

Figure 1 shows a schematic flow diagram of a method for comprehensive recovery of smelting wastewater containing magnesium according to a preferred embodiment of the present invention.

Embodiments

It should be noted that embodiments and the features in embodiments in the application may be combined with each other without conflict. Hereinafter, the present invention will be described in detail with

As mentioned in the background art section, the treatment method of the smelting wastewater containing magnesium in the prior art is either too high for the cost of treatment or the treated wastewater is limited in recycling for the high salt content. In order to improve the above-described situation in the prior art, in a typical embodiment of the invention, as shown in Fig. 1, there is provided a method for comprehensive recovery and recycling of smelting wastewater containing magnesium, which comprises: adjusting the pH of the smelting wastewater containing magnesium to 10.0 to 12.5 with a basic substance as a neutralizing agent to obtain a slurry containing magnesium hydroxide and calcium sulfate; wherein the smelting wastewater containing magnesium is the wastewater containing magnesium sulfate; the basic substance being a basic substance containing calcium; and step S2, introducing carbon dioxide gas into the slurry containing magnesium hydroxide and calcium sulfate to perform carbonization, and performing solid-liquid separation to the carbonized slurry to obtain a solid slag and a magnesium bicarbonate solution.

For the smelting wastewater containing magnesium, the above method comprises adjusting the pH of the smelting wastewater to 10.0 to 12.5 by adding a basic substance containing calcium (including the basic substance containing calcium and magnesium) as the neutralizing agent to the smelting wastewater. In this process, the added calcium-containing basic substance in the smelting wastewater is removed by generating calcium sulfate precipitation in the role of H and SO₄', while the Mg in the wastewater is converted into magnesium hydroxide. The carbon dioxide gas is then introduced into the slurry containing magnesium hydroxide and calcium sulfate to conduct carbonization treatment to convert the magnesium hydroxide in the waste water into soluble

2_|_ magnesium bicarbonate while the remaining small amount of free Ca in the wastewater is converted into calcium carbonate and further separating with magnesium ions, and thus make the separation of calcium ion in recycled magnesium bicarbonate solution is more thorough, significantly reducing the content of CaSO₄ in recycled water, so as to effectively solve the problem of scaling of pipelines, conveying pumps, storage tanks and the like, while the resulting magnesium bicarbonate solution is used for the smelting separation process, not only achieve recycling the production wastewater, but also achieve zero discharge of wastewater.

The wastewater containing magnesium sulphate treated in the above method includes, but is not limited to, wastewater containing magnesium sulfate produced by subjecting monazite, xenotime, bastnaesite, nickel cobalt ore and other ores to sulphate calcining, water leaching, magnesium oxide neutralization and impurity removal and extraction-transformation process during smelting separation. Wastewater containing magnesium sulfate produced during the separation of any ore can be recycled by the above-mentioned method of the present invention.

In the step SI described above, there are various ways to adjust the pH of the wastewater to 10.0 to 12.5 by adding the basic substance as the neutralizing agent, and the specific adjustment mode can be appropriately adjusted according to the actual production demand. In a preferred embodiment of the present invention, when the smelting wastewater containing magnesium is acidic wastewater containing magnesium sulfate, the above step S1 comprises the steps of: step Sil, adjusting the pH of the smelting wastewater containing magnesium to 4.0 to 10.0 with the basic substance containing calcium to obtain a solid-liquid mixture; step S12, filtering the solid-liquid mixture to obtain a filtrate; step S13, adjusting the pH of the filtrate to 10.0 to 12.5 with the basic substance containing calcium to obtain the slurry containing magnesium hydroxide and calcium sulfate.

In the preferred embodiment described above, the purpose of adjusting the pH of the smelting wastewater containing magnesium to 4.0 to 10.0 with a basic substance containing calcium to obtain the solid-liquid mixture is mainly to neutralize the H⁺ in the smelting wastewater while reducing the content of calcium sulfate in cycle water, so as to minimize the problem of pipe fouling arising in recycling the recovered water. Thus, all basic substances containing calcium capable of providing a basic environment and readily converting calcium therein into calcium sulfate to be removed are suitable for use in the present invention. It is preferable to use calcium hydroxide, and the source of calcium hydroxide is not limited to the solid powder of calcium hydroxide, but also the basic calcium hydroxide obtained by reacting calcium oxide obtained by calcining calcium oxide or calcium carbonate with water. From the point of considering the treatment cost of the smelting wastewater and the recycling of raw materials, the basic substance containing calcium is preferably the basic substance containing calcium hydroxide prepared by using raw material of limestone (or dolomite) which is rich in natural and inexpensive.

Likewise, the basic substance containing calcium and magnesium refers to a mixture containing calcium hydroxide and magnesium hydroxide at the same time, which may be a mixture containing calcium hydroxide and magnesium hydroxide obtained by reacting a calcined product of an ore containing calcium and magnesium or an industrial waste containing calcium and magnesium with water, or a mixture containing calcium hydroxide and magnesium hydroxide obtained by digestion of light-burned dolomite.

In the preferred embodiment described above, adjusting the pH of the smelting wastewater to 4.0 to 10.0 with the basic substance containing calcium can both neutralize the large amount of H⁺ in the smelting wastewater and the separate calcium from the wastewater in form of calcium sulfate. After adjusting the pH of the smelting wastewater to 4.0 to 10.0 with the basic substance containing calcium to the solid-liquid mixture, filter the solid-liquid mixture, and remove the precipitated calcium sulfate to obtain a filtrate, followed by adjusting the pH of the filtrate to 10.0 to 12.5 with the basic substance containing calcium and magnesium or the basic substance containing calcium. By controlling the addition amount of the neutralizing agent of basic substance containing calcium and the pH value, the calcium and magnesium ions in the waste water are precipitated step by step, and the pH value of the filtrate after removing calcium sulfate is controlled in the range of 10.0 to 12.5 to make the Mg in the smelting wastewater convert into magnesium hydroxide under the basic condition containing calcium and/or magnesium to obtain a slurry containing magnesium hydroxide and calcium sulfate precipitate. The specific reactions occurred are as follows:

2H⁺(liquid)+SO4²'( liqiiid)+Ca(OH)2(solid)^CaSO₄(solid)+H₂O(liqiiid) Mg²⁺( liquid)+SO4²'( liquid)+Ca(OH)2(solid)~* Mg(OH)₂(solid)+CaSO₄(solid)

In the preferred embodiment described above, adjusting the pH of the smelting wastewater containing magnesium to 4.0 to 10.0 with a basic substance containing calcium has been able to achieve the purpose of precipitating calcium sulphate. In order to make precipitation easier occur or precipitate be more thoroughly, in another preferred embodiment of the present invention, the step SI further comprises the step of adding a calcium sulfate seed crystal to the smelting wastewater containing magnesium; and/or the step of subjecting the slurry containing magnesium hydroxide and calcium sulfate to an aging treatment. Adding the calcium sulphate seed crystal is facilitated to form the precipitation of calcium sulfate more easily and makes the precipitation reaction relatively thoroughly. And the aging treatment can also make the precipitation relatively thoroughly. The specific time of the aging may be appropriately adjusted according to the amount of the treated smelting wastewater. In a preferred embodiment of the present invention, the time of the aging treatment is less than or equal to 6 h. The aging time less than or equal to 6 h has been able to make calcium sulfate precipitate enough thoroughly, conducive to reuse the treated water, if the aging time is continued to be extended, it will lead to delay the overall process operation and not conducive to conduct the overall process of the process.

The wastewater which is recycled by the present invention is the wastewater containing magnesium sulfate. The wastewater mainly contains Mg²⁺, H⁺ and SO4²', and may also include one or more of Na⁺, Cf and NO3‘. The wastewater system is complex with a wide range of impurity ions. When the basic substance containing calcium is adopted to treat the wastewater, calcium ions may present in the form of calcium sulfate precipitation in the system of sulfate ions, forming a solid mixture with magnesium hydroxide and entering into the carbonization step. In the carbonation process, if there is a large amount of calcium ions in the system, it will induce bicarbonate to produce calcium carbonate crystal, reducing the production rate of magnesium bicarbonate, and leading to the decomposition of magnesium carbonate into magnesium carbonate solid to dissolve out. A large number of scaling has great impact on the continuous production.

Therefore, the present invention produces a low activity and stable crystalline calcium sulfate precipitate with a reasonable control of the pH value during the alkali conversion process, which reduces the calcium ion concentration in the alkali converted water phase, and the low activity calcium sulfate is not easy to resolve into calcium ions to reduce the carbonization rate. In the preferred embodiment described above, by segmentation control of pH value, the segmentation alkali conversion of calcium ions and magnesium ions is achieved, and then the purpose of removing the partial calcium is first achieved by solid-liquid separation, so that the calcium ion concentration in the aqueous phase at the beginning of the carbonization is reduced. And by further adding seed crystal and/or aging treatment, the calcium ions are precipitated more thoroughly in the segmentation alkali conversion precipitation, so that the calcium ion concentration in the aqueous phase at the beginning of the carbonization is lower and the carbonation is better.

In the above carbonization step, the purpose of carbonization is to convert the magnesium hydroxide in the slurry into soluble magnesium bicarbonate while further removing the remaining calcium ions in the slurry by the formation of calcium carbonate. The amount of carbon dioxide introduced in the step of carbonization can therefore be appropriately adjusted according to the amount of wastewater to be treated. In a preferred embodiment of the present invention, the step S2 described above comprises introducing carbon dioxide gas into the slurry to perform carbonization and controlling the pH of the slurry in the range of 6.5 to 8.0 during the carbonization to obtain a carbonized slurry; and performing solid-liquid separation to the carbonized slurry to obtain the solid slag and the magnesium bicarbonate solution.

The wastewater treated by the above-mentioned neutralization and precipitation is a mixed slurry containing Mg(OH)₂ and CaSO₄, and contains a small amount of free Ca , OH' and SO₄ ' due to the micro-solubility of CaSO₄. Carbon dioxide gas is used to convert the solid Mg(OH)₂ into Mg(HCO₃)₂ solution. The free Ca in the aqueous phase is converted into CaCO₃ precipitation due to the presence of a large amount of HCO₃‘, which promotes the solidification transformation of calcium, achieving the purpose of further removal of calcium in aqueous phase. The specific reaction of the carbonation process is as follows:

Mg(OH)₂(solid)+2CO₂(gas)-^Mg(HCO₃)₂(liquid)

Ca²⁺+2HCO₃-*CaCO₃(solid)+H₂O(liquid)+CO₂(gas)

The following side reaction may occur during this carbonation reaction:

Mg(OH)₂(solid)+CO₂(solid)+H₂O—MgCO₃ · 3H₂O(solid)

In the preferred embodiment described above, the amount of carbon dioxide introduced is controlled by controlling the pH of the slurry in the range of 6.5 to 8.0, and the calcium ions in the slurry can be precipitated and removed as much as possible in the form of calcium carbonate to achieve separation of calcium and magnesium, so that the calcium ion concentration in magnesium bicarbonate solution is minimized. The calcium ion concentration in the magnesium bicarbonate solution obtained by solid-liquid separation is 0.01 g/L to 0.7 g/L, preferably 0.01 g/L to 0.4 g/L by using the carbonization step of the above embodiment.

The lower the calcium ion concentration in the magnesium bicarbonate solution is, the more difficult to cause pipe fouling when reused as recycled water, achieving the recycling of the smelting wastewater.

In the preferred embodiment described above, the time of carbonization may be appropriately adjusted depending on the amount of calcium ions in the slurry containing magnesium hydroxide. In still another preferred embodiment of the present invention, it is preferable that the time of carbonization in the carbonization step is 10 min to 120 min, more preferably 20 min to 60 min. The time of carbonization treatment is controlled in the range of 10 min to 120 min, which can not only achieve removing the remaining calcium ions in the slurry containing magnesium hydroxide, but also make the time of the whole treatment process of wastewater be not too long, which will also affect the cycle running period and reduce the treatment effectiveness. If the time of carbonization is too long, it is possible not only to convert calcium ions precipitated as calcium carbonate into calcium bicarbonate due to excessive carbon dioxide and difficult to remove, but also easily lead to longer processing cycle, affecting the treatment efficiency of smelting wastewater. And if the carbonization time is shorter than 10 min, it is very likely that the precipitate of calcium ions is not thorough enough, so that the calcium ion concentration in the treated cycling water is high, which is not conducive to the recycling of treated water. And the time of carbonization is controlled within 20min ~ 60min, so that the calcium ion concentration in the treated magnesium bicarbonate solution is lower, and the treatment time is relatively shorter, which is beneficial to the efficient recycling of the wastewater in enterprise.

The above-mentioned method provided by the present invention embodies the reasonable utilization of energy from various aspects, and the above-mentioned step S2 is no exception. In another preferred embodiment of the present invention, as shown in Fig. 1, the solid slag obtained in the above step S2 is purified to obtain calcium sulfate, and the specific purification treatment includes a sulfuric acidification method as shown in Fig. 1. In practical applications, the specific ways of purification may be selected according to the specific production conditions and equipments. The purified calcium sulphate can be sold as a product in order to maximize its value. In another specific embodiment, the solid slag is returned to neutralize the wastewater produced by smelting separation.

In the above step of carbonizing by introducing in carbon dioxide gas (as shown in Fig. 1), the source of the carbon dioxide gas introduced in may be one or more gases of boiler flue gas, calcined kiln gas of oxalate precipitation and carbonate precipitation and the gas produced by saponification extraction of the magnesium bicarbonate solution. As shown in Fig. 1, the present invention preferably obtains a carbon dioxide-containing gas by applying compression, purification or other treatment steps to the gas produced in the above processes as raw materials, not only to achieve the purpose of carbonizing the solution containing magnesium hydroxide using carbon dioxide to get a magnesium bicarbonate solution, but also to use the process gas reasonably, which is low-carbon and discharge reduction, in line with environmental requirements.

In the above step S2, the magnesium bicarbonate solution obtained by the treatment of smelting wastewater containing magnesium can be reused as cycle water (as shown in Fig. 1). Thus, all the procedures using water or the procedures using weakly alkaline solution in the separation and smelting processes of ores can be carried out by using the magnesium bicarbonate solution provided by the above-described method of the present invention. That is, the magnesium bicarbonate solution obtained by the above-mentioned method can be used in one or more of ore sulfating calcining-water leaching-neutralization and impurity removal procedure, acid leaching-neutralization and impurity removal procedure, solution extraction-transformation or precipitation-transformation procedure, solution extraction-separation procedure and/or solution precipitation procedure. For example, it can be used in sulfating calcining-water leaching-neutralization and impurity removal procedure of Baotou rare earth ore concentrate, transformation and extraction procedure of Baotou ore rare earth, acid leaching-neutralization and impurity removal procedure of Sichuan bastnaesite and ionized rare earth ore and extraction separation procedure of rare earth and precipitation procedure of rare earth solution, to achieve recycling.

The beneficial effects of the present invention will be further described below in connection with specific examples.

EXAMPLE 1

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding calcium hydroxide (wherein the calcium hydroxide was obtained by reacting quicklime and water) to the wastewater to bring the pH of the wastewater to 10.0 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate and the pH of the slurry after carbonization was controlled to 7.3. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution.

The solid slag was purified by sulfuric acidification to obtain calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.7 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 2

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding a mixture containing calcium hydroxide and magnesium hydroxide (obtained by reacting light burned dolomite and water) to the wastewater to bring the pH of the wastewater to 11.0 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.62 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 3

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding calcium hydroxide (wherein the calcium hydroxide was obtained by reacting quicklime and water) to the wastewater to bring the pH of the wastewater to 11.5 to obtain a slurry containing magnesium hydroxide and calcium sulfate with a alkalinity of 0.24mol/L.

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to carbonize for 60 min and the pH of the slurry after carbonization was controlled to 7.3. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution with magnesium bicarbonate concentration of 3.15g/L (calculated in MgO). The carbonization rate was 65.7%.

The solid slag was purified by sulfuric acidification to obtain calcium sulfate which can be used for the preparation of cement.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.56 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 4

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding a mixture containing calcium hydroxide and magnesium hydroxide (obtained by reacting light burned dolomite and water) to the wastewater to bring the pH of the wastewater to 12.5 to obtain a slurry containing magnesium hydroxide and calcium sulfate with a alkalinity of 0.37mol/L.

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate and the pH of the slurry after carbonization was controlled to 7.3. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution with magnesium bicarbonate concentration of 5.55g/L (calculated in MgO). The carbonization rate was 65.7%.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.45 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 5

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding calcium hydroxide (wherein the calcium hydroxide was obtained by reacting quicklime and water) to the wastewater to bring the pH of the wastewater to 12.5 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate and the pH of the slurry after carbonization was controlled to 7.5. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.4 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution, extraction separation, and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 6

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to carbonize for 120 min and the pH of the slurry after carbonization was controlled to 6.5. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.58 g/L, and the magnesium bicarbonate solution was returned to use for leaching, neutralization and impurity removal, extraction and transformation procedure of rare earth solution and extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 7

The wastewater containing magnesium sulfate produced by extraction separation of nickel cobalt solution of sulfuric acid was taken as the treatment object. A reaction was carried out by adding calcium hydroxide (wherein the calcium hydroxide was obtained by reacting quicklime and water) to the wastewater to bring the pH of the wastewater to 12.5 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to carbonize for 40 min and the pH of the slurry after carbonization was controlled to 8.0. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.38 g/L, and the magnesium bicarbonate solution was returned to extraction separation procedure of the nickel cobalt solution of sulfuric acid.

EXAMPLE 8

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding calcium hydroxide to the wastewater to bring the pH of the wastewater to 12.5 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by treating the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate and the pH of the slurry after carbonization was controlled to 7.0. The carbonized slurry was subjected to solid-liquid separation to obtain a solid slag and a magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.49 g/L, and the magnesium bicarbonate solution was returned to use for precipitation transformation procedure of rare earth solution, extraction separation procedure of rare earth solution and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

COMPARATIVE EXAMPLE 1

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding calcium hydroxide to the wastewater to bring the pH of the wastewater to 9.5 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 1.0 g/L, and the magnesium bicarbonate solution was returned to use for extraction and transformation procedure of rare earth solution, extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

COMPARATIVE EXAMPLE 2

The wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding calcium hydroxide to the wastewater to bring the pH of the wastewater to 13.0 to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 1.1 g/L, and the magnesium bicarbonate solution was returned to use for extraction and transformation procedure of rare earth solution, extraction separation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 9

The acidic wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding quicklime to the waste water and the pH of the wastewater was adjusted to 5.0 to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate;

and the pH value of the filtrate was adjusted to 12.5 by adding quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.3 g/L, and the magnesium bicarbonate solution was returned to use for acid bleaching-neutralization and impurity removal procedure of Baotou rare earth ore concentrate, extraction separation procedure of rare earth solution and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 10

The acidic wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 5.0 with digested quicklime to obtain a solid-liquid mixture. After 6 h of aging, the solid-liquid mixture was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 12.5 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.22 g/L, and the magnesium bicarbonate solution was returned to use for acid bleaching-neutralization and impurity removal procedure of Baotou rare earth ore concentrate, and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 11

The acidic wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 5.0 with digested quicklime to obtain a solid-liquid mixture. After 2 h of aging, the solid-liquid mixture was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 7.5 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.24 g/L, and the magnesium bicarbonate solution was returned to use for acid bleaching-neutralization and impurity removal procedure of Baotou rare earth ore concentrate, and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 12

The acidic wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 5.0 with digested quicklime to obtain a solid-liquid mixture. After 0.5 h of aging, the solid-liquid mixture was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 12.5 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.27 g/L, and the magnesium bicarbonate solution was returned to use for acid bleaching-neutralization and impurity removal procedure of Baotou rare earth ore concentrate, and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 13

The acidic wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding quicklime to the waste water and calcium sulphate seed crystal was added during reaction, adjusting the pH to 5.0 to obtain a solid-liquid mixture. The solid-liquid mixture was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 12.5 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.25 g/L, and the magnesium bicarbonate solution was returned to use for acid bleaching-neutralization and impurity removal procedure of Baotou rare earth ore concentrate, and precipitation procedure of rare earth solution of Baotou rare earth ore concentrate.

EXAMPLE 14

The acidic wastewater containing magnesium sulfate produced by subjecting the monazite ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 4.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 11.5 with digested light-burned dolomite to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of boiler flue gas, calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 7.3 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution.

The carbonized slurry was subjected to solid-liquid separation to obtain a magnesium bicarbonate solution and a solid slag of calcium carbonate precipitation.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.33 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution and precipitation procedure of rare earth solution of monazite ore concentrate.

The solid slag was returned to use for the neutralization of acidic wastewater in the smelting separation of rare earth ore.

EXAMPLE 15

The acidic wastewater containing magnesium sulfate produced by subjecting the monazite ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 6.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 11.5 with digested light-burned dolomite to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The carbonized slurry was subjected to solid-liquid separation to obtain a magnesium bicarbonate solution and a solid slag containing calcium sulfate and calcium carbonate precipitation.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.3 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of rare earth solution and precipitation procedure of rare earth solution of monazite ore concentrate.

EXAMPLE 16

The acidic wastewater containing magnesium sulfate produced by subjecting the rare earth solution of sulfuric acid to extraction separation was taken as the treatment object. The pH of the wastewater was adjusted to 9.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 11.5 with digested light-burned dolomite to obtain a slurry containing magnesium hydroxide and calcium sulfate with a alkalinity of 0.67mol/L.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of boiler flue gas, calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 7.3 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution with magnesium bicarbonate concentration of 12.2g/L (calculated in MgO). The carbonization rate was 91.5%.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.18 g/L, and the magnesium bicarbonate solution was returned to use for extraction separation procedure of the rare earth solution of sulfuric acid and precipitation procedure of rare earth solution.

EXAMPLE 17

The acidic wastewater containing magnesium sulfate produced by subjecting the rare earth solution of sulfuric acid to extraction and transformation and extraction separation was taken as the treatment object. The pH of the wastewater was adjusted to 10.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 11.5 with digested light-burned dolomite to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.08 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of smelting separation of the rare earth solution of sulfuric acid.

EXAMPLE 18

The acidic wastewater containing magnesium sulfate produced by subjecting the rare earth solution of sulfuric acid to extraction separation was taken as the treatment object. The pH of the wastewater was adjusted to 4.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 10.0 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 7.5 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.65 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of smelting separation of the rare earth solution of sulfuric acid.

EXAMPLE 19

The acidic wastewater containing magnesium sulfate produced by subjecting the rare earth solution of sulfuric acid to extraction separation process was taken as the treatment object. The pH of the wastewater was adjusted to 4.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 11.0 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of boiler flue gas, calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 7.5 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.58 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of smelting separation of the rare earth solution of sulfuric acid.

EXAMPLE 20

The acidic wastewater containing magnesium sulfate produced by subjecting the nickel cobalt solution of sulfuric acid to extraction separation process was taken as the treatment object. The pH of the wastewater was adjusted to 4.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 12.0 with digested quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.4 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of extraction separation of the nickel cobalt solution of sulfuric acid.

EXAMPLE 21

The acidic wastewater containing magnesium sulfate produced by subjecting the mixed ore concentrate of monazite and xenotime to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal procedure-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 10.0 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 12.5 with digested light-burned quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of boiler flue gas, calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 6.5 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.5 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of rare earth smelting separation of the mixed ore concentrate of monazite and xenotime.

EXAMPLE 22

The acidic wastewater containing magnesium sulfate produced by subjecting the mixed ore concentrate of xenotime to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal procedure-extraction and transformation process was taken as the treatment object. The pH of the wastewater was adjusted to 3.5 with digested quicklime to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 11.5 with digested light-burned quicklime to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of boiler flue gas, calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 8.0 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.36 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of rare earth separation of the mixed ore concentrate of xenotime.

COMPARATIVE EXAMPLE 3

The acidic wastewater containing magnesium sulfate produced by subjecting the mixed ore concentrate of xenotime to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal procedure-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding quicklime to the wastewater and the pH was adjusted to 11.0 to obtain large amount of solid-liquid mixture(wherein most of magnesium forms precipitate) which was subjected to solid-liquid separation to obtain a filtrate. The pH of the filtrate was adjusted to 12.5 with digested light-burned dolomite to obtain a slurry containing magnesium hydroxide and calcium sulfate.

Carbon dioxide (wherein the carbon dioxide was obtained by comprehensive recovery of boiler flue gas, calcined kiln gas of rare earth oxalate and carbonate and the gas produced by saponification extraction of the magnesium bicarbonate solution) was introduced into the slurry containing magnesium hydroxide and calcium sulfate to take carbonization and the pH was controlled to 8.0 to obtain carbonized slurry containing calcium sulfate and calcium carbonate precipitation, and magnesium bicarbonate solution with magnesium bicarbonate concentration of 0.54g/L.

The result of the test showed that the calcium ion concentration in the magnesium bicarbonate solution was 0.14 g/L, and the magnesium bicarbonate solution was returned to use for the process recycle of rare earth separation of the mixed ore concentrate of xenotime.

COMPARATIVE EXAMPLE 4

The acidic wastewater containing magnesium sulfate produced by subjecting the Baotou rare earth ore concentrate to sulfating calcining-water leaching-magnesium oxide neutralization and impurity removal procedure-extraction and transformation process was taken as the treatment object. A reaction was carried out by adding quicklime to the wastewater containing magnesium and the pH was adjusted to 6.0-9.0 to obtain a solid-liquid mixture which was subjected to solid-liquid separation to obtain a filtrate and a waste slag. The calcium ion concentration in the filtrate was 1.1 g/L. When the filtrate was recycled, the scaling of calcium sulfate and the like was easy to occur in pipelines, delivery pumps or storage tanks with the change of the temperature, which seriously affected the recycling of the wastewater and had a great impact on the continuous production.

From the above description, it can be seen that the above-mentioned examples of the present invention achieves the following technical effects:

(1) by the two key steps of neutralizing precipitation and carbonization purification, the Mg²⁺ in the non-saponified acidic wastewater of the sulfuric acid system is converted into magnesium bicarbonate solution; the Ca in the wastewater is converted into calcium sulfate and a small amount of calcium carbonate, achieving more thorough separation of calcium ions and magnesium ions, significantly reducing the content of CaSO₄ in recycled water, so as to effectively solve the problem of scaling of pipelines, conveying pumps, storage tanks and the like.

(2) the magnesium bicarbonate solution prepared by carbonizing may be used for water bleaching, neutralization and impurity removal, saponification, extraction separation and other procedures, so as to realize closed-loop utilization of wastewater and achieve near-zero discharge, saving a lot of water resource.

(3) the by-product of calcium sulfate in whole process has stable property, no effect on the environment; and can be further purified to achieve commercial gypsum specification.

It can be said that the present invention can obtain a magnesium bicarbonate solution by carrying out precipitation transformation and carbonization purification steps to smelting wastewater containing magnesium and then the solution is returned to smelting separation procedure of the rare earth, which can not only achieve comprehensive recycling of the wastewater during smelting process of the rare earth, but also achieve zero discharge of production wastewater. The resource utilization of entire technology route is high, and its economic and social benefits are very obvious.

The acidic wastewater containing magnesium and calcium discharged from the rare earth enterprise is recycled comprehensively with the alkali conversion carbonation method of the present invention, which can not only reduce the sewage charge but also can return the treated pure magnesium bicarbonate solution to use for neutralization and

2016266463 21 Jun 2019 impurity removal of the rare earth solution, extraction separation of rare earth by saponification of organic phase, precipitation preparation of rare earth carbonate and other procedures, achieving wastewater recycling and zero discharge of production sewage.

The examples described above are only preferred examples of the present invention and is not intended to limit the present invention, and various changes and modifications may be made by one skilled in the art. Any modifications, equivalent substitutions, improvements and the like within the spirit and principle of the present invention are intended to be io included within the scope of the present invention.

Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the 15 exclusion of any other integer or group of integers.

2016266463 21 Jun 2019

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method for comprehensive recovery of smelting wastewater containing magnesium, comprising the steps of:

step SI, comprising steps Sil, S12 and S13;

step Sil, adjusting the pH of the smelting wastewater containing magnesium to 4.0 to 10.0 with a basic substance containing calcium to obtain a solid-liquid mixture, wherein the smelting wastewater containing magnesium is acidic wastewater containing magnesium sulfate;

step SI2, filtering the solid-liquid mixture to obtain a filtrate; and step S13, adjusting the pH of the filtrate to 10.0 to 12.5 with the basic substance containing calcium to obtain a slurry containing magnesium hydroxide and calcium sulfate; and step S2, introducing carbon dioxide gas into the slurry containing magnesium hydroxide and calcium sulfate to perform carbonization, and performing solid-liquid separation of the carbonized slurry to obtain a solid slag and a magnesium bicarbonate solution.
2. The method according to claim 1, wherein the smelting wastewater containing magnesium is wastewater containing magnesium sulfate produced by sulfation calcination, water leaching, magnesium oxide neutralization and impurity removal and extraction-transformation process during smelting and separation.
3. The method according to claim 1 or 2, wherein the step SI further comprises the step of adding a calcium sulfate seed crystal to the smelting wastewater containing magnesium; and/or the step of subjecting the

2016266463 21 Jun 2019 slurry containing magnesium hydroxide and calcium sulfate to an aging treatment.
4. The method according to claim 3, wherein in the step of subjecting the slurry containing magnesium hydroxide and calcium sulfate to an aging treatment, the aging time is 0.5 h to 6 h.
5. The method according to any one of claims 1 to 4, wherein the step S2 comprises the steps of:

introducing carbon dioxide gas into the slurry containing magnesium hydroxide and calcium sulfate to perform carbonization and controlling the pH of the slurry in the range of 6.5 to 8.0 during the carbonization to obtain a carbonized slurry; and performing solid-liquid separation to the carbonized slurry to obtain the solid slag and the magnesium bicarbonate solution.
6. The method according to any one of claims 1 to 5, wherein the calcium ion concentration in the magnesium bicarbonate solution is 0.01 g/L to 0.7 g/L.
7. The method according to claim 6, wherein the calcium ion concentration in the magnesium bicarbonate solution is 0.01 g/L to 0.4 g/L.
8. The method according to any one of claims 1 to 7, wherein the solid slag is subjected to acidizing treatment to produce calcium sulphate or is returned to neutralize the acidic wastewater produced by the smelting and separation to produce calcium sulphate.
9. The method according to any one of claims 1 to 8, wherein the carbon dioxide gas is produced from a process exhaust gas comprising one or

2016266463 21 Jun 2019 more of boiler flue gas, calcined kiln gas of oxalate precipitation and carbonate precipitation and the gas produced by saponification extraction of magnesium bicarbonate solution.
10. The method according to any one of claims 1 to 9, wherein in the step S2, the magnesium bicarbonate solution is used in a wet smelting procedure, wherein the smelting procedure is one or more of ore sulfating calcining-water leaching-neutralization and impurity removal procedure, acid leaching-neutralization and impurity removal procedure, solution extraction-transformation or precipitation transformation procedure, solution extraction separation procedure and solution precipitation procedure.