JP2008043872A - Method for judging end point of formation reaction of precipitated sulfide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for judging an end point of a formation reaction of precipitated sulfide, in which the end point of the formation reaction, which is not judged sufficiently only by measuring an ORP (an oxidation-reduction potential), can be judged correctly at a step of separating a heavy metal as precipitated sulfide of the heavy metal and recovering the separated sulfide. <P>SOLUTION: When the end point of such the formation reaction that the heavy metal is precipitated as its sulfide by using a sulfurizing agent to the extent of the objective concentration of the heavy metal is judged, the ORP is measured and simultaneously the concentration of hydrogen sulfide (H<SB>2</SB>S) gas in the upper part of a reaction tank is measured. Since hydrogen sulfide is generated suddenly at the end point of the formation reaction and thereafter in the formation reaction of precipitated sulfide, the end point of the formation reaction is judged by combining the concentration of hydrogen sulfide gas with the conventional ORP. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for determining a reaction end point of a sulfurized precipitate formation in which a heavy metal is precipitated using a sulfurizing agent in a step of separating and recovering heavy metal by sulfide precipitate generation.

  Conventionally, the formation of sulfide precipitates in which heavy metals are precipitated by a sulfurizing agent such as sodium hydrosulfide, sodium sulfide, and hydrogen sulfide has been widely used in hydrometallurgy and wastewater treatment. For example, in Japanese Patent Application Laid-Open No. 2004-105833, when heavy metals in wastewater are removed by precipitation with a sulfiding agent, the ORP (oxidation-reduction potential) of the treatment liquid is continuously measured by an ORP sensor, and based on the obtained ORP value. A method of adding an appropriate amount of a sulfurizing agent is described.

  However, in the sulfidation-precipitation reaction in which heavy metals are precipitated using a sulfiding agent such as sodium hydrosulfide, sodium sulfide, hydrogen sulfide, etc., the form of metal ions and the form of sulfur components change depending on the pH of the treated water. Due to the complexity, it was difficult to accurately determine the end point of the reaction that causes heavy metals to precipitate to the target concentration.

  For example, in the case of waste liquid generated from a factory such as a copper smelting plant, a pH meter and an ORP meter are installed in the reaction tank and are constantly monitored in order to treat liquids containing multiple heavy metals and liquids with different pHs. The end point of the reaction is determined based on the potential measured with an ORP meter. However, due to the occurrence of errors due to scaling and electrode deterioration, the ORP measurement value is usually not constant, and it is necessary to confirm the excess or deficiency of the sulfurizing agent by electrode cleaning or simple beaker test at regular intervals. It was.

In addition, when processing a solution having a low pH, since the form of hydrogen sulfide (H ₂ S) is stable, it is easy to cause a situation in which a sulfurizing agent is excessively added due to a slight potential difference. There is a danger that hydrogen sulfide gas is generated in large quantities. For this reason, the reaction tank is provided with a device that sucks and removes the gas generated by the reaction, but it is also possible that hydrogen sulfide gas having a design concentration or higher may be generated. In addition, as a specific substance of hydrogen sulfide, an allowable concentration is 10 ppm.
JP 2004-105833 A

  In view of the above-described conventional circumstances, the present invention can accurately determine the end point of a reaction, which is not sufficient only by measurement with an ORP meter in the separation and recovery process of heavy metal by sulfide precipitation. An object is to provide a method for determining a reaction end point.

  In order to achieve the above-mentioned problem, the present inventors have repeatedly studied a method capable of accurately determining the end point of the sulfur precipitation reaction, and as a result, found that the reaction end point of the sulfur precipitation reaction is accompanied by rapid hydrogen sulfide generation. The present invention has been achieved.

  That is, the method for determining the reaction end point of sulfide precipitation formation provided by the present invention is a method for determining the end point of the reaction for precipitating heavy metal to a target concentration using a sulfurizing agent in the heavy metal separation and recovery step by sulfide precipitation formation. Simultaneously with the measurement of ORP, the hydrogen sulfide gas concentration in the upper part of the reaction vessel is measured.

  In the method for determining the reaction end point of sulfide precipitation formation in the present invention, the heavy metal separation and recovery process is continuously and automatically operated by controlling the addition amount of the sulfiding agent based on the ORP measurement and the hydrogen sulfide gas concentration measurement. Features.

  According to the present invention, by measuring the hydrogen sulfide gas concentration in the upper part of the reaction tank simultaneously with the measurement value by the ORP meter, it becomes possible to accurately determine the reaction end point of the sulfide precipitation generation. As a result, it is possible to prevent an increase in sulfiding agent cost due to excessive addition of the sulfiding agent and minimize the generation of toxic hydrogen sulfide gas, thereby preventing deterioration or danger of the working environment around the reaction vessel. it can.

In the method for determining the reaction end point of sulfide precipitation formation according to the present invention, for example, as shown in FIG. 1, a processing stock solution containing heavy metals and a sulfiding agent are continuously supplied to the reaction tank 1 to sulphide heavy metals and sulfides in the processing stock solutions. Carry out sulfidation precipitation reaction with an agent. At that time, pH and ORP are continuously monitored by a pH meter and an ORP meter installed in the reaction tank 1, and at the same time, gas at the top of the reaction tank 1 is continuously sucked and introduced into the H ₂ S measuring instrument 2 and hydrogen sulfide. Continuously measure the gas concentration.

  The sulfidation precipitation reaction can be carried out in the same manner as in the prior art, and as the sulfiding agent, usual ones such as sodium hydrosulfide, sodium sulfide and hydrogen sulfide can be used. The addition adjustment of the sulfiding agent can be easily performed by controlling the control valve in the same manner in the case of liquid sulfiding agent such as sodium hydrosulfide and sodium sulfide and hydrogen sulfide gas. Further, the exhaust gas from the reaction tank 1 is sucked and supplied to the detoxification tower 3 periodically or continuously to remove harmful components and then released into the atmosphere.

The pH and ORP in the sulfidation precipitation reaction are determined in advance for various waste liquids by a beaker test. Usually, since the potential at which precipitation is completed is known for each type of heavy metal, the treatment is started from this value, and the beaker is used. Start continuous operation by running in parallel with the test. Moreover, in measuring the hydrogen sulfide gas concentration, the gas in the reaction vessel can be diluted to be a sample gas in accordance with the measurement range of the H ₂ S measuring instrument to be used.

  For example, in wastewater such as a copper smelting process, Cu, As, Zn, Cd, etc. are mainly the main components of the contained heavy metals. Since Cu and As are precipitated at a potential higher than that of Zn and Cd, Cd is mainly selected as a target for determining the end point of the sulfur precipitation reaction. In addition, since the potential at the end of the sulfidation reaction varies depending on the pH, the pH is usually controlled to be constant using an acid or alkali.

  For Cd, the higher the concentration is, the more the amount of neutralizing agent used in the later wastewater treatment process is increased. Therefore, lowering the concentration in the sulfidation precipitation process reduces the cost. Usually, the ORP in the waste liquid having a pH of about 2 is about -50 mV, but in the case of a liquid having a sulfuric acid concentration of about 100 g / l or more, the Cd residual concentration is lowest at about +50 mV. For Zn, the precipitation rate varies greatly depending on the pH, but even a high-concentration liquid can be easily removed by the neutralization coagulation precipitation method in the wastewater treatment of the final step, so it is not necessary to completely separate it in the sulfide precipitation step. .

  The end point of the sulfide precipitation reaction is determined based on the measurement result of the hydrogen sulfide gas concentration in the upper part of the reaction tank and the measurement result of the ORP. In the case of a normal processing stock solution close to neutrality, the sulfide precipitation reaction can be stably carried out by maintaining a constant pH, so that the ORP reaches the set value and the hydrogen sulfide gas at the top of the reaction vessel When the concentration exceeds the set concentration, it can be accurately determined that the reaction is the end point.

  In the case of a pH drop for some reason, or in the case of a processing stock solution having a low pH, it is extremely difficult to determine the end point by using ORP alone. However, when the hydrogen sulfide gas concentration in the upper part of the reaction tank exceeds the set concentration, the end point is determined. Determine and reduce or stop the addition of sulfurizing agent. By controlling in this way, it is possible to prevent the addition of an excessive sulfiding agent, and it is possible to prevent the risk that a large amount of highly toxic hydrogen sulfide gas is generated.

Waste metal from the copper smelting process was used as a processing stock solution, and hydrogen sulfide gas was used as a sulfiding agent to generate sulfide precipitation of heavy metals. In this processing stock solution, the main heavy metal components and their concentrations are 0.5 g / l for Cu, 0.5 g / l for As, 0.8 g / l for Zn, and 0.6 g / l for Cd, The H ₂ SO ₄ concentration was 147 g / l and the pH was 0.

  In the sulfidic precipitation reaction of heavy metals in the treatment stock solution, ORP and residual Cd concentrations were continuously measured, and the results obtained are shown in FIG. From the results of FIG. 2 showing the relationship between the ORP and the residual Cd concentration, it can be seen that when the ORP is +50 mV, the residual Cd concentration is constant and the sulfidation precipitation reaction is completed.

Further, in the above sulfidation precipitation reaction, the gas inside the reaction vessel was sampled and the hydrogen sulfide gas concentration was measured simultaneously with the ORP measurement, and the obtained results are shown in FIG. From FIG. 3 showing the relationship between the ORP and the hydrogen sulfide (H ₂ S) gas concentration, the potential of ORP + 50 mV, recognized as the end point of the reaction from FIG. 2, is the same as the potential at which a large amount of H ₂ S gas starts to be generated. I understand that.

It is a schematic diagram of the reaction apparatus used for a sulfide precipitation reaction. It is a graph which shows the relationship between ORP and residual Cd density | concentration. It is a graph showing the relationship between the ORP and _{H 2} S gas concentration.

Explanation of symbols

1 reaction tank 2 H ₂ S measuring instrument 3 abatement tower

Claims (2)

  Measure the hydrogen sulfide gas concentration at the top of the reaction tank at the same time as the ORP measurement when determining the end point of the reaction for precipitating heavy metals to the target concentration using a sulfurizing agent in the process of separating and recovering heavy metals by sulfide precipitation. A method for determining a reaction end point characterized by: 2. The method for determining a reaction end point according to claim 1, wherein the heavy metal separation and recovery step is continuously and automatically operated by controlling an addition amount of a sulfiding agent based on the ORP measurement and the hydrogen sulfide gas concentration measurement.

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