DE19603449C2 - Process for the production of calcium carbonate from calcium-containing combustion residues of residues from paper production - Google Patents

Description

This invention relates to a process for producing calcium carbonate from Calcium-containing combustion residues from in papermaking falling residues.

Residual materials must be used at high landfill costs or additional payments be deposited or recycled. To the landfill or disposal or To keep recycling costs as low as possible, these residues burned, which leads to a weight reduction and thus to a reduction resulting in the above-mentioned costs. For example, the Incineration of residues from paper production, based on the dry amount of residue, to a weight reduction of about 50 to 60%. Because of these both economic and environmental benefits of Weight reduction usually takes the burning of residues taking advantage of the high calorific values of the residues, too, which inevitably leads to leads to an increasing accumulation of combustion residues. This burn However, residues must also be incurred with high landfill costs or additional payments are deposited or recycled.

Previous studies have shown that, for example, combustion residues of the residues accumulating in particular in papermaking partially contain over 20 wt .-% calcium. Other main ingredients are Silicon, aluminum and magnesium, which are mostly considered water-insoluble Connections exist. The source of the high calcium levels in the combus Residual residue is calcium carbonate, which is increasingly used as a filler and coating pigment is used in paper production and finishing.  

In addition to the natural calcium carbonate from the chalk formation (CCN), synthetic precipitated calcium carbonate (CCP) is also used. This is due to the high temperatures of the waste incineration process Calcium partly as calcium oxide and partly as water-insoluble calcium connections, e.g. B. calcium silicates, before, and is therefore particularly for Papermaking no longer usable.

CCP is manufactured on an industrial scale by burning limestone. After this Quenching the calcium oxide with water, the suspension is cleaned and with the carbon dioxide from the burning process carbonized. By varying the Precipitation parameters (temperature, concentration, precipitation time) and aftertreatment lung such. B. grinding, depending on the intended use, special modifications ions and qualities.

EP 0 480 587 A2 describes the production of precipitated calcium carbonate by slaking quicklime and then precipitating the product by carbonizing the aqueous solution.

CCP is increasingly used in paper production because CCP compared to natural chalk by a higher degree of whiteness and a characterized by better opacity and reduced consumption of optical Brightening leads.

The present invention is therefore based on the object of a new method ren for the production of synthetic, precipitated calcium carbonate with Ver To provide calcium-containing residues, which makes the cost-intensive ve landfill of such residues can be further reduced and that in calcium contained in the residues at the same time by recovery in form of high-quality calcium carbonate, for example in paper production and - Refinement can be used again as a raw material substitute.

This object is characterized by those characterized in claims i to 15 Features resolved.  

In particular, a process for producing calcium carbonate is carried out Calcium-containing starting materials are provided, comprising the steps:

• (a) Suspending the calcium-containing starting products in an aqueous Solution,
• (b) separating the substantially non-soluble components of these first Suspension for obtaining a first solution containing calcium ions and
• (c) precipitating calcium carbonate from the first solution containing calcium ions, wherein one or more carbonate ions generating before and / or in step (c) Compounds are added, the precipitation in step (c) at a pH of greater than 7 is carried out and as combustion starting materials residues from residues from paper production will.

The combustion residues from the rest of the paper production contain substances as starting products of the process according to the invention for example over 20% by weight of calcium, some of which is calcium oxide and / or is present as water-insoluble calcium compounds such as calcium silicates.

The term "calcium carbonate" includes synthetic, precipitated calcium carbonate (CCP).

In step (a) of the process according to the invention, the starting products are suspended, the term “suspending” meaning the mixing or dispersing of the starting products with water or an aqueous solution in a suitable device at a suitable temperature, for example in the range from 15 to 80 ° C. , preferably from 20 to 30 ° C. When the combustion residues of residues from paper production are suspended in water, the suspension usually has a pH greater than 7 due to the high calcium oxide content. In such a suspension, the calcium oxide dissolves as Ca ²⁺ and 20H⁻. To increase the stability of such a suspension, suspending aids such as surfactants can be added.

The test results of analyzes are exemplary in Tables 1 and 2 of some incineration residues from paper manufacturing Residues shown.

Table 1

Examination results of combustion residues (see sample codes) of residual materials from paper production

Table 2

Examination results of combustion residues (see VR1 to VR3) of residues from paper production

In one embodiment according to the invention, this first suspension of Step (a) has a pH of less than 7, which also causes compounds such as Calcium silicates, which are essentially insoluble in a basic medium, in dissolved form may be present. The pH of less than 7 can by  Adding at least one acidic agent to this first suspension or by suspending the residues in at least one acidic agent tend aqueous solution can be adjusted. The acidic agent is preferred an inorganic acid, such as HCl or HNO₃, or an organic acid or a mixture of them.

It happens due to the high temperatures of the waste incineration processes through decomposition of the mineral residues, such as. B. kaolin and Calcium carbonate, to reactive oxide mixtures, such as. B. alumina, Silicon oxide and calcium oxide, which in turn form a water-insoluble compound applications such as B. calcium silicate can implement. These water soluble ver Bonds, especially calcium silicate, are at least partially in an acidic environment soluble.

In step (b) of the process according to the invention, the are essentially Insoluble components of this first suspension to obtain a first Calcium ion-containing solution separated. The term "essentially non-solvable Liche ingredients "includes those after suspending the starting products insoluble solid particles of the suspension.

In a preferred embodiment of the method according to the invention the separated, essentially non-soluble components in one aqueous solution at a pH of less than 7, preferably less than 3, most preferably at a pH in the range of 1 to 2 and at one Suspen temperature in the range of 15 to 80 ° C, preferably from 20 to 30 ° C. diert and the substantially insoluble components of these second suspensions sion separated to obtain a second calcium ion-containing solution. Of the pH of less than 7 can be achieved by adding at least one acidic one Agent to this second suspension or by suspending the separated essentially non-soluble ingredients in at least one acidic Agent-containing aqueous solution can be adjusted. The acidic agent is preferably carbon dioxide or carbonic acid, an inorganic acid such as HCl or HNO₃, or an organic acid or a mixture thereof.  

The term "separation" encompasses physical separation processes, such as filtration, Centrifugation or sedimentation, to obtain the first or second calciu ion-containing solution. Preferably, the separation takes place essentially Chen insoluble constituents of the first suspension and / or the essence non-soluble components of the second suspension by filtration, where, depending on the filtration device, a pressure of, for example 2.5 × 10³ to 7 × 10⁵ Pa can be applied.

In a preferred embodiment of the method according to the invention the second solution containing calcium ions before step (c) with the first calcium ion-containing solution from step (b) to obtain a third calcium ion content united solution.

In one embodiment of the method according to the invention, the two th calcium ion-containing solution and / or the third calcium ion-containing solution Solution before step (c) one or more carbonate ions conditions, such as carbon dioxide, carbonic acid or a salt of carbonic acid, such as alkali, Alkaline earth or ammonium carbonates or bicarbonates, in one, ins especially for the precipitation to be carried out in the following step (c) sufficient concentration, preferably in excess, based on the dissolved Calcium, can be added.

In another embodiment of the method according to the invention the first solution containing calcium ions and / or the second calcium ions containing solution and / or the third calcium ion-containing solution before step (c) at least one basic agent, such as NaOH, KOH, Ca (OH) ₂ or NH₃, in a sufficient concentration to set a pH of greater than 7, preferably greater than 7.5 and more preferably at a pH in Range from 7.5 to 9.5 can be added.

In step (c) of the process according to the invention, calcium carbonate is obtained from the first solution containing calcium ions and / or second solution containing calcium ions Solution and / or third solution containing calcium ions at a pH of  greater than 7, preferably greater than 7.5, and more preferably one pH in the range of 7.5 to 9.5 and at a temperature in the range of 20 to 50 ° C, preferably from 20 to 30 ° C.

The term "precipitation" or "precipitation" includes the excretion of calcium as a calcium carbonate precipitate. The felling is done by adding a or several precipitants, such as the carbonate-generating compounds, and / or by adjusting the pH and / or the temperature, where the solubility product of calcium carbonate in the precipitation solution is exceeded.

The basic agent defined above and / or the one defined above Carbonate-generating compound can also be introduced in step (c) and / or maintaining the precipitation process in sufficient concentration tration of the precipitation solution are added, the precipitation solution being a pH greater than 7, preferably greater than 7.5 and more preferred has a pH in the range of 7.5 to 9.5.

After the precipitation step, the calcium carbonate thus obtained is removed from the precipitation Solution by methods known in the art, such as filtration or Centrifugation, separated and drying, for example at 105 ° C, subject.

The precipitation solution, if appropriate after suitable preparation, can be used for for example through ion exchange or membrane technology (e.g. "osmosis" or "reverse osmosis"), at least partially to suspend the output products separated in step (a) and / or to suspend those in step (b) ten, essentially insoluble constituents can be used. Preferential the process water of the process according to the invention becomes wise in one closed circuit.

Fig. 1 is a schematic representation of an apparatus for performing the method according to the invention.

The present invention is explained in more detail by the following example.

The combustion residue used in this example shows the following composition (main components):
Calcium: 20.5% by weight
Magnesium 3.0% by weight
Silicon 15.4% by weight
Aluminum 10.1% by weight
Chloride 280 mg / kg
Sulfate: 40 mg / kg

3 L of deionized water were placed in the coolable and heatable stainless steel dissolving container ( 1 ) and 150 g of the combustion residue were added with stirring. The temperature of the suspension was adjusted to 30 ° C (± 2 ° C) using a thermocouple and a controller. The conductivity was continuously measured during the stirring process at a speed of 60 min ^-1 . When there was no significant increase in conductivity, the stirring process was stopped and the filtration started. After closing the lid of the release container ( 1 ), a pressure of 2 × 10⁵ Pa was applied. The suspension was filtered through a glass frit, which is arranged in the bottom of the dissolving container, into a collecting container ( 2 ) and the filtrate was transferred to a 4 L storage container ( 3 ). The resulting calcium ion-containing solution showed the following parameters:
pH: 12.3
Conductivity: 400 mS / m
Total dry residue: 3200 mg / L
dissolved calcium: 450 mg / L

The water-insoluble residue ("filter residue") which remained in the dissolving container ( 1 ) was then mixed with 3 L of a 0.5 M HCl solution. This suspension was also kept between 28 and 32 ° C. As Rührge speed 60 min ^{-1 were} set again. The stirring process was ended after about 30 minutes. The HCl-soluble fraction was again separated from the solid by filtration under the conditions listed above. The resulting filtrate was transferred to a second, 4 L holding container ( 4 ) to obtain a second calcium ion containing the solution.

For the subsequent precipitation, the solutions containing calcium ions from the storage containers ( 3 ) and ( 4 ) were combined in the precipitation container ( 5 ). A concentrated NaOH solution was added via a metering device until a pH of 9 was reached. The contents of the precipitation container were stirred at a speed of 120 min ^-1 . CO₂ was introduced into the solution at a volume flow of about 50 L / h from a compressed gas bottle with a reducing valve. In order to keep the pH in a weakly alkaline state, concentrated NaOH solution was metered in during the precipitation. After about 50 min, the introduction of CO₂ was stopped and the precipitated solid was separated from the aqueous phase by means of a filtration device ( 6 ). To check the full stability of the precipitation, CO₂ was again introduced into the aqueous phase, with no further precipitation being found. The aqueous phase was returned to the solution container ( 1 ) via a line and process water purification device.

The weight of the solid dried at 105 ° C. to constant weight was 68.1 g. X-ray microanalytical and acidimetric analysis showed that the precipitated solid consists of almost 100% calcium carbonate.

Claims (16)

1. A method for producing calcium carbonate from calcium-containing starting products, comprising the steps:

• (a) suspending the calcium-containing starting products in an aqueous solution,
• (b) separating the substantially insoluble constituents of this first suspension to obtain a first solution containing calcium ions and
• (c) precipitating calcium carbonate from the first solution containing calcium ions,

wherein one or more carbonate-generating compounds are added before and / or in step (c), characterized in that the precipitation in step (c) is carried out at a pH of greater than 7 and that combustion residues of at residues from paper production are used. 2. The method of claim 1, wherein the separated, substantially non-soluble components of the starting products in an aqueous Solution are suspended at a pH of less than 7, which in essential non-soluble components of this second suspension Obtaining a second solution containing calcium ions are separated and this second solution containing calcium ions before step (c) with the first Calcium ion-containing solution from step (b) to obtain a third Cal cium ion-containing solution is combined. 3. The method according to claim 1 or 2, wherein the suspension of step (a) has a pH of less than 7.   4. The method according to any one of claims 1 to 3, wherein the first suspension Sion and / or an acidic agent is added to the second suspension. 5. The method according to any one of claims 1 to 4, wherein the aqueous solution in step (a) and / or essentially to suspend the Insoluble ingredients used an acidic aqueous solution Agent contains. 6. The method according to claim 4 or 5, wherein the acidic agent carbon dioxide, an inorganic acid or an organic acid or a mixture of it is. 7. The method according to claim 6, wherein the inorganic acid HCl or HNO₃ is. 8. The method according to any one of claims 1 to 7, wherein the separation of the im essential non-soluble components of the first suspension and / or the essentially non-soluble components of the second suspension done by filtration. 9. The method of claim 8, wherein the filtration is carried out under pressure becomes. 10. The method according to any one of claims 1 to 9, wherein the first calcium ion-containing solution and / or the second calcium ion-containing solution and / or the third solution containing calcium ions before step (c) basic agent is added. 11. The method according to claim 10, wherein the basic agent NaOH, KOH, Ca (OH) ₂ or NH₃ or a mixture thereof. 12. The method according to any one of claims 1 to 11, wherein also the second Calcium ion-containing solution and / or the third calcium ion-containing solution  Solution before and / or in step (c) one or more Carbonate-generating compounds are added. 13. The method according to any one of claims 1 to 12, wherein the Carbonate-producing compound carbon dioxide or a salt of Is carbonic acid. 14. The method according to any one of claims 1 to 13, wherein the precipitated Cal cium carbonate is separated from the precipitation solution and a dry voltage is subjected. 15. The method according to claim 14, wherein the precipitation solution, if appropriate after suitable preparation, at least partially to suspend the Residues in step (a) and / or for suspending those in step (b) separated, essentially insoluble constituents becomes.