JP7540267B2 - Method for cleaning filter cloth of liquid filter - Google Patents

Description

The present invention relates to a method for cleaning the filter cloth of a liquid filter. More specifically, the present invention relates to a method for cleaning the filter cloth in a liquid filter such as a continuous liquid filter, in order to eliminate the decrease in the amount of liquid passing through the filter cloth due to clogging of the filter cloth to an acceptable level.

An example of a liquid filter to which the present invention can be applied is a continuous liquid filter (see Patent Document 1), which is widely used as a device for filtering liquid containing zinc sulfide in a nickel smelting process (see Figure 3) using high pressure sulfuric acid leaching (HPAL) to recover nickel from low-grade nickel oxide ore.

If liquid continues to pass through the liquid filter for a certain period of time or more, the filter cloth becomes clogged with solid matter, causing a decrease in the amount of liquid passing through. In this case, the liquid passing through the filter cloth is temporarily stopped, and a cleaning process (hereinafter also referred to as "backwash") is carried out to remove the solid matter clogging the filter cloth after the treatment liquid in the tank is temporarily transferred from the repeating section to the outside of the liquid filter.

JP 2013-185179 A

However, in the above-mentioned liquid filter, even if the conventional filter cloth cleaning method called "backwash" is performed, it is difficult to completely remove the clogged filter cloth. Even if the filter cloth is periodically cleaned in this manner, the decrease in the amount of liquid passing through the filter cloth over time due to the accumulation of clogged filter cloth is still unavoidable, and in order to maintain the amount of liquid passing through the filter cloth over the long term, it is necessary to periodically replace the filter cloth.

The present invention aims to suppress the accumulation of clogging in the filter cloth in liquid filters such as continuous liquid filters, thereby reducing the frequency of periodic replacement of the filter cloth.

The inventors discovered that when cleaning the filter cloth in a liquid filter such as a continuous liquid filter, the above problem can be solved by performing a step of discharging a small amount of a portion of the treatment liquid into a downstream device prior to the step of transferring the liquid out of the liquid filter, and thus completed the present invention. Specifically, the present invention provides the following.

(1) A method for cleaning a filter cloth in a liquid filter, the method comprising: a treatment tank, a filter cloth, and a liquid discharge mechanism, the liquid discharge mechanism having a filtrate discharge section for discharging filtrate, a repeating section for repeating a portion of the liquid in the treatment tank to a device arranged on the upstream process side, and a residue discharge section for discharging liquid containing solids separated by filtration, the method comprising: a first treatment liquid discharge step for discharging a portion of the entire treatment liquid stored in the treatment tank, which has a relatively high solid concentration, from the residue discharge section after the supply of the treatment liquid to the treatment tank is stopped; a second treatment liquid discharge step for returning another portion of the treatment liquid, which remains in the treatment tank after the first treatment liquid discharge step, from the repeating section to a device arranged on the upstream process side; and a cleaning step for injecting a cleaning liquid into the treatment tank and cleaning the filter cloth with the cleaning liquid after the second treatment liquid discharge step.

(2) The method for cleaning the filter cloth of a liquid filter described in (1), in which the shape of the lower part of the treatment tank is such that the horizontal cross-sectional area gradually decreases toward the deepest part, and the residue discharge part is joined to the deepest part of the treatment tank.

(3) The method for cleaning a filter cloth of a liquid filter described in (1) or (2), in which, in the second treatment liquid discharge step, the treatment liquid is discharged until the entire filter cloth is exposed to the gas phase, and, in the cleaning step, an inert gas is sprayed onto the filter cloth before the cleaning liquid is injected.

(4) A method for cleaning a filter cloth of a liquid filter according to any one of (1) to (3), in which the discharge amount of the treatment liquid in the first treatment liquid discharge step is controlled by controlling the height of the liquid level detected on the top side of the treatment tank.

(5) A method for cleaning the filter cloth of a liquid filter according to any one of (1) to (4), in which the device arranged on the upstream process side is a sulfurization reaction tank and the solid matter is a sulfide.

According to the present invention, in a liquid filter such as a continuous liquid filter, the accumulation of clogging in the filter cloth can be suppressed, and the frequency of periodic replacement of the filter cloth can be reduced.

1 is a cross-sectional view showing a schematic configuration of a liquid filter to which the filter cloth cleaning method of the present invention can be applied. FIG. 2 is a flow chart showing the process flow of the filter cloth cleaning method of the present invention. FIG. 2 is a process diagram of a hydrometallurgical method for nickel oxide ore, which is a specific example of a process in which the liquid filter of FIG. 1 is used. FIG. 4 is a flow chart showing a partial process of the hydrometallurgical refining method of nickel oxide ore in FIG. 3, which is a process flow of a dezincing step performed using the liquid filter shown in FIG. 1.

The following describes an embodiment of the present invention. However, the present invention is not limited to the following embodiment. The present invention is applicable to a liquid filter that includes a treatment tank, a filter cloth, and a liquid discharge mechanism, and further includes a repeating section that repeats a portion of the treatment liquid to a device located on the upstream process side (see Figure 1).

<Liquid filter>
An example of a liquid filter to which the filter cloth cleaning method for a liquid filter according to the present invention can be applied is a liquid filter 10 shown in Fig. 1. As shown in Fig. 1, the liquid filter 10 is provided with a treatment tank 1, a filter cloth 2, a treatment liquid supply mechanism 3, a liquid discharge mechanism 4, a cleaning liquid supply mechanism 5, an inert gas injection mechanism 6, a liquid level detection mechanism 7, an exhaust mechanism 8, and a control mechanism (not shown) that controls the operation of each of the above mechanisms provided in the liquid filter 10.

As a representative example of a preferred embodiment, the liquid filter 10 can be implemented as a continuous liquid filter used in a nickel recovery process using high pressure sulfuric acid leaching (hereinafter, HPAL: abbreviation for High Pressure Acid Leach). Details of the nickel recovery process using high pressure sulfuric acid leaching (hereinafter, HPAL: abbreviation for High Pressure Acid Leach) will be described later.

[Treatment tank]
The treatment tank 1 is a tank for storing the treatment liquid, and in this tank, the treatment liquid is filtered by the filter cloth 2. The treatment tank 1 is preferably a sealed tank in which the pressure inside the tank can be adjusted to an appropriate pressure to promote the permeation of the treatment liquid into the filter cloth 2.

[Filter cloth]
A filter cloth 2 is placed inside the treatment tank 1. The treatment liquid (which means a liquid (solid-liquid mixture) containing a certain amount of solid matter as impurities to be filtered; the same applies below) is filtered by this filter cloth 2 to obtain a filtrate from which impurities have been removed.

[Processing liquid supply mechanism]
The treatment liquid supply mechanism 3 supplies a treatment liquid into the treatment tank 1. For example, when the liquid filter 10 is used in the dezincing step of the hydrometallurgical method for nickel oxide ore shown in Fig. 3, a solid-liquid mixture containing zinc sulfide is supplied from the treatment liquid supply mechanism 3 into the treatment tank 1 as a treatment liquid.

[Liquid discharge mechanism]
The liquid discharge mechanism 4 discharges the filtrate from which impurities have been removed and the treatment liquid containing residue to the outside of the treatment tank 1. The liquid discharge mechanism 4 of the liquid filter 10 includes a filtrate discharge section 41 that discharges the filtrate, a repeating section 42 that repeats a portion of the treatment liquid to a device arranged on the upstream process side, and a residue discharge section 43 that discharges the liquid containing solids separated by the filtration process (solid-liquid mixture).

The above-mentioned "device located on the upstream process side", i.e., the device that repeats a portion of the treated liquid, may be a device capable of transferring liquid to the treatment tank 1, such as a storage tank for the treated liquid, and is not limited to a specific device. For example, if the liquid filter 10 is a filter that separates sulfides as solids from the treated liquid, the sulfurization reaction tank located on the upstream process side can be the "device located on the upstream process side" that repeats a portion of the treated liquid.

During normal operation, the residue discharge section 43 discharges the treatment liquid containing the solid matter adhering to the filter cloth 2 after filtration. However, as described below, after the cleaning process for cleaning the filter cloth, the cleaning liquid used for cleaning is discharged from the residue discharge section 43 together with the solid matter peeled off from the filter cloth by cleaning.

For example, similar to the above, when the liquid filter 10 is used in the dezincification step of the hydrometallurgical method for nickel oxide ore shown in FIG. 3, the dezincification liquid, which is the mother liquor for nickel recovery containing nickel and cobalt, is discharged from the filtrate discharge section 41. In addition, although it is not necessary to use the repetition section 42 during normal operation, in the second treatment liquid discharge step, a portion of the treatment liquid containing zinc sulfide is repetitively sent from the repetition section 42 to the dezincification reaction tank.

[Cleaning liquid supply mechanism]
The cleaning liquid supply mechanism 5 supplies cleaning liquid into the treatment tank 1 when cleaning the filter cloth 2. It is preferable that the cleaning liquid supply mechanism 5 is provided at its tip with a spray nozzle capable of spraying the cleaning liquid onto the filter cloth 2.

[Inert gas injection mechanism]
The inert gas injection mechanism 6 injects an inert gas such as nitrogen into the treatment tank 1 when cleaning the filter cloth 2. The inert gas injection mechanism 6 may be provided with a spray nozzle at its tip, which can spray gas onto the filter cloth 2.

[Liquid level detection mechanism]
The liquid level detection mechanism 7 is a mechanism for detecting the liquid level of the processing liquid inside the processing tank 1. The liquid level detection mechanism 7 is preferably configured by a combination of a plurality of detection devices each of which detects a liquid level independently defined at a different height. Specifically, the liquid level detection mechanism 7 is preferably configured to include at least an upper limit detection device 71 that detects that the liquid level of the processing liquid inside the processing tank 1 has reached a specified "upper limit", and a lower limit detection device 72 that detects that the liquid level has reached a specified "lower limit". In addition, each detection device (71, 72) can be configured by appropriately using various conventionally known liquid level detection devices, specifically, a vibration type level switch, an optical sensor, etc.

[Exhaust mechanism]
The exhaust mechanism 8 exhausts gas from the gas phase of the treatment tank 1 to the outside of the treatment tank 1 in the liquid filter 10. For example, similarly to the above, when the liquid filter 10 is used in the dezincification step of the hydrometallurgical method for nickel oxide ore shown in Fig. 3, the gas in the gas phase of the treatment tank 1 is exhausted through the exhaust mechanism 8 while the treatment tank 1 is filled with the treatment liquid. Furthermore, the exhaust mechanism 8 often functions in conjunction with the environmental smoke collection equipment for the entire plant.

<Method for cleaning filter cloth of liquid filter>
The filter cloth cleaning method for a liquid filter of the present invention (hereinafter also referred to as the "filter cloth cleaning method") is a filter cloth cleaning method that can be preferably applied to the above-mentioned liquid filter 10. However, the "filter cloth cleaning method for a liquid filter" of the present invention is a filter cloth cleaning method that can be applied to liquid filters of various other configurations, not limited to the above-mentioned liquid filter 10, so long as the liquid filter is a liquid filter in which a filter cloth is disposed in a tank, and has, as a liquid discharge mechanism, a mechanism for discharging the filtrate and solids separated by filtration, as well as a repeating part that repeats a portion of the treatment liquid in a device disposed on the upstream process side.

As shown in FIG. 2, the filter cloth cleaning method is different from the conventional backwash cleaning method in that, after the supply of the processing liquid to the processing tank 1 is stopped, a "first processing liquid discharge step st1" is performed in which a high concentration portion of the processing liquid stored in the processing tank 1, which is a portion of the entire processing liquid and has a relatively high solid concentration, is discharged from the residue discharge section 43. This is preceded by a "second processing liquid discharge step st2" in which most of the processing liquid is returned from the repetition section 42 to a device located on the upstream process side, and then a "cleaning step st3" is performed in the same manner as the conventional backwash cleaning method.

[First processing liquid discharge step]
In the first treatment liquid discharge process st1, after the supply of the treatment liquid into the treatment tank 1 is stopped, a high-concentration portion, which is a portion of the entire treatment liquid stored in the treatment tank 1 and has a relatively high solid concentration, is discharged from the residue discharge section 43.

Here, in the treatment tank 1, a solid-liquid mixture with a relatively high solid content concentration among the entire treatment liquid stored therein usually remains in the deepest part 11 of the tank (see FIG. 1). In this case, the part of the treatment liquid that remains near the deepest part 11 of the tank is the "high concentration part of the treatment liquid". Therefore, if the residue discharge part 43 is connected to the deepest part 11 of the treatment tank, this "high concentration part of the treatment liquid" can be preferentially discharged from the residue discharge part 43. If the connection part of the residue discharge part 43 to the treatment tank 1 and the part where the "high concentration part of the treatment liquid" remains are separated, a pipe for collecting residue can be extended between the residue discharge part 43 and the part in question, so that the "high concentration part of the treatment liquid" can be preferentially discharged.

The filter cloth cleaning method is particularly effective when the shape of the lower part of the treatment tank 1 is one in which the horizontal cross-sectional area gradually decreases toward the deepest part 11, and when the residue discharge part 43 is joined to the deepest part 11 of the treatment tank 1. This is because the smaller the horizontal cross-sectional area of the part, the higher the solid concentration tends to be, and the more efficiently the "solids" can be discharged.

In addition, in the first treated liquid discharge step st1, the amount of treated liquid discharged from the residue discharge section 43 is preferably controlled based on the liquid level detected, for example, by the upper limit detection device 71 at the top side of the treatment tank 1, by controlling the liquid level to fall until it reaches a predetermined height.

[Second processing liquid discharge step]
In the second processing liquid discharge step st2, after the first processing liquid discharge step st1 is performed, i.e., after the "high concentration portion of the processing liquid" is preferentially discharged, the processing liquid remaining in the processing tank 1 is returned from the repeating section 42 to an apparatus arranged on the upstream process side. In the second processing liquid discharge step st2 performed after the first processing liquid discharge step st1, the processing liquid returned to the apparatus arranged on the upstream process side is a solid-liquid mixture with a relatively low solid content concentration. Moreover, it is more preferable that this processing liquid is a residual liquid that does not substantially contain solid content.

In the second treatment liquid discharge step st2, it is preferable to discharge the treatment liquid described above until the entire filter cloth 2 is exposed to the gas phase. This discharge amount is preferably controlled, for example, based on the liquid level detected by the lower limit detection device 72, by controlling the liquid level to be allowed to drop until the liquid level reaches a predetermined height.

[Cleaning process]
In the washing step st3, after the second treatment liquid discharge step st2 is performed, a washing liquid is injected from the washing liquid supply mechanism 5 into the treatment tank 1 to wash the filter cloth 2 with the washing liquid. It is preferable to use warm water as the washing liquid in order to avoid unwanted reactions.

In addition, in the cleaning step st3, it is preferable to spray an inert gas such as nitrogen from the inert gas injection mechanism 6 onto the filter cloth 2 before injecting the cleaning liquid in order to remove any deposits on the surface of the filter cloth.

<Method for hydrometallurgy of nickel oxide ore>
Finally, an outline of a "hydrometallurgy method for nickel oxide ore" that is a typical industrial process that can be carried out using a liquid filter to which the filter cloth washing method of the present invention is applied is described below. This "hydrometallurgy method for nickel oxide ore" is a hydrometallurgy method for recovering nickel and cobalt from a slurry of nickel oxide ore by, for example, a high-temperature, high-pressure leaching process (HPAL process).

As shown in Figure 3, the hydrometallurgical method for nickel oxide ore is a method in which the following steps are carried out in sequence: "ore preparation process" in which an ore slurry is obtained from a mixture of multiple types of low-grade nickel oxide ores; "leaching process" in which the ore slurry is mixed with heated and pressurized sulfuric acid to leach nickel into sulfuric acid and the residual free acid in the leachate is pre-neutralized to obtain a leachate slurry; "solid-liquid separation process" in which a leachate (pregnant liquor) is obtained from the leachate slurry by solid-liquid separation; "neutralization process" in which the pregnant liquor obtained by solid-liquid separation is neutralized; "dezincification process" in which zinc is removed from the neutralized liquor; and "nickel sulfurization process" in which the dezincification liquor is recovered as a nickel-cobalt mixed sulfide by using hydrogen sulfide gas. The leach residue slurry separated in the "solid-liquid separation process" is sent to a tailings dam after its components are adjusted in the final neutralization process to a form suitable for long-term deposition in nature. In addition, after nickel sulfide is recovered in the nickel sulfidation process, part of the barren liquid is reused in the solid-liquid separation process, and the excess is sent to the final neutralization process.

In the "dezincing step", as shown in FIG. 4, the neutralized liquid obtained in the "neutralization step" is introduced into a sulfurization reaction tank (dezincing reaction tank), and a sulfurizing agent such as hydrogen sulfide gas or sodium hydrosulfide is added to sulfurize the zinc contained in the neutralization end liquid. Then, the dezincing end liquid (nickel recovery mother liquid containing nickel and cobalt) is obtained by solid-liquid separation in a liquid filter (see FIG. 4). In the dezincing reaction tank, zinc sulfide based on the zinc contained in the neutralization end liquid is generated by adding hydrogen sulfide gas. Then, the zinc sulfide and the nickel recovery mother liquid are separated from the treatment liquid containing the slurry-like zinc sulfide by a liquid filter (continuous liquid filter). As a result, the end liquid (dezincing end liquid) after the treatment in the dezincing step becomes the nickel recovery mother liquid from which the zinc has been removed.

In a factory operating by the above-mentioned nickel oxide ore hydrometallurgy method, when the treatment liquid had a pH of 2.8 to 3.2 and the liquid flow rate was 100 to 200 m ³ /hr, the filter cloth was replaced once every 10 to 25 days (about 15 days on average) when using a conventional backwash method. However, as a result of a test operation in which the filter cloth washing method was changed to the filter cloth washing method of the present invention, it was confirmed that the filter cloth replacement frequency could be reduced to about once every 15 to 30 days (about 20 days on average).

REFERENCE SIGNS LIST 1 Treatment tank 11 Deepest part (of treatment tank) 12 Top part (of treatment tank) 2 Filter cloth 3 Treatment liquid supply mechanism 4 Liquid discharge mechanism 41 Filtrate discharge section 42 Repeat section 43 Residue discharge section 5 Cleaning liquid supply mechanism 6 Inert gas injection mechanism 7 (71, 72) Liquid level detection mechanism 8 Exhaust mechanism 10 Liquid filter st1 First treatment liquid discharge step st2 Second treatment liquid discharge step st3 Cleaning step

Claims (5)

A method for cleaning a filter cloth in a liquid filter, comprising: a treatment tank; a filter cloth; and a liquid discharge mechanism, the liquid discharge mechanism having a filtrate discharge section for discharging a filtrate, a repeating section for repeating a treatment liquid containing solid matter in the treatment tank to a device disposed on an upstream process side , and a residue discharge section for discharging a liquid containing solid matter separated by a filtration process, the method comprising:
a first treated liquid discharge step of discharging a part of the entire treated liquid stored in the treatment tank, the part being a high concentration part of the treated liquid having a relatively high solid content concentration, from the residue discharge part without returning the part to the device arranged on the upstream process side after the supply of the treated liquid into the treatment tank is stopped;
a second processing liquid discharge step of returning a low-concentration portion of the processing liquid having a relatively low solid content concentration, which is a remaining portion of the entire processing liquid remaining in the processing tank after the first processing liquid discharge step, from the repetition section to the device disposed on the upstream process side;
a washing step of injecting a washing liquid into the treatment tank and washing the filter cloth with the washing liquid after the second treatment liquid discharge step;
Do the following in this order :
A method for cleaning the filter cloth of a liquid filter. The shape of the lower part of the treatment tank is such that the horizontal cross-sectional area gradually decreases toward the deepest part, and the residue discharge part is joined to the deepest part of the treatment tank.
The method for cleaning the filter cloth of a liquid filter according to claim 1. In the second treatment liquid discharge step, the treatment liquid is discharged until the entire filter cloth is exposed to a gas phase,
In the washing step, before the washing liquid is poured, an inert gas is blown onto the filter cloth.
A method for cleaning the filter cloth of a liquid filter according to claim 1 or 2. In the first treatment liquid discharge step, the discharge amount of the treatment liquid is controlled by controlling the height of the liquid level detected on the top side of the treatment tank.
A method for cleaning the filter cloth of a liquid filter according to any one of claims 1 to 3. The apparatus arranged on the upstream process side is a sulfurization reaction tank,
The solid is a sulfide.
A method for cleaning the filter cloth of a liquid filter according to any one of claims 1 to 4.

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