A process for removing chlorine from a solution of zinc sulphate containing chlorine by means of ozone or ozone air

Abstract

The application discloses a method for removing chlorine from a zinc sulfate solution containing chlorine by using ozone or ozone air, and ozone or ozone air generated by an ozone generator is introduced into a closed pressure-adjustable container containing the zinc sulfate solution containing chlorine, and oxidation dechlorination is carried out in the container at normal temperature or under the natural temperature condition of the solution; low-chlorine zinc sulfate solution and mixed waste gas containing oxygen and chlorine gas are obtained; the mixed waste gas is introduced into saturated limewater or a sodium alkali solution, and chemical products of sodium hypochlorite or calcium hypochlorite are obtained. The application adopts ozone or ozone air to remove chlorine from the zinc sulfate solution containing chlorine, and has the advantages of simple process, high dechlorination efficiency, comprehensive recovery of chemical products of calcium hypochlorite or sodium hypochlorite for reuse or sale, less waste, no sodium chloride accumulation, and good social and economic benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydrometallurgy, and particularly relates to a method for removing chlorine from a high-chlorine-containing zinc sulfate solution by ozone and comprehensively recovering calcium hypochlorite or sodium hypochlorite chemical products. BACKGROUND

[0002] In the hydrometallurgical process of zinc, because the zinc oxide raw material or zinc sulfide raw material inevitably contains a certain amount of chlorine component, the chlorine component will inevitably enter the solution together with zinc sulfate during acid leaching, and it is difficult to remove and enrich once it enters the solution. When the chlorine ion in the solution reaches 500 mg / L or more, it will endanger the electrolytic production of zinc metal or affect the quality of zinc sulfate heptahydrate chemical products. Therefore, the hydrometallurgical process of zinc must remove the chlorine component to below 500 mg / L, and the lower the better.

[0003] At present, the main technologies for removing chlorine in the hydrometallurgical process of zinc are pyrometallurgical and hydrometallurgical methods. The pyrometallurgical method mainly roasts high-chlorine-containing zinc raw materials at 900 DEG C or more to decompose zinc chloride and other chlorides, so that the chlorine is volatilized and removed in the form of chlorine gas or hydrogen chloride gas. For example, multi-chamber roasting or rotary kiln roasting, which can decompose and remove more than 95% of chlorides, but the equipment investment is large, the energy consumption is high, the roasting dust pollution is large, the treatment is difficult, the dechlorination is not complete, and the wet dechlorination technology needs to be supplemented in production.

[0004] The main hydrometallurgical dechlorination technologies include alkali washing of chlorine-containing raw materials, such as washing with 5% or so sodium carbonate or sodium hydroxide aqueous solution or washing with lime water; metal chloride salt precipitation, such as cuprous chloride precipitation or silver chloride, mercury chloride precipitation; N235 extraction of chlorine ions or P204 extraction of zinc ions or ion exchange method. The above-mentioned hydrometallurgical dechlorination processes not only have complex processes and high production costs, but also have large amounts of wastewater, which is difficult to discharge up to standard. In addition, the sodium chloride produced by dechlorination has complex composition, low quality, low industrial utilization value, poor economic value, and is not easy to sell and reuse, and the inventory is serious. SUMMARY

[0005] In order to overcome the shortcomings of the above-mentioned processes, the present application proposes a method for removing chlorine from a chlorine-containing zinc sulfate solution by ozone or ozone air, which not only has simple technology and process, high dechlorination efficiency, but also can comprehensively recover calcium hypochlorite or sodium hypochlorite chemical products for reuse or sale, so that the three wastes are less, there is no sodium chloride accumulation, and the social and economic benefits are good.

[0006] The technical scheme of the present application:

[0007] A method for removing chlorine from a chlorine-containing zinc sulfate solution by ozone or ozone air, characterized in that the specific implementation steps are as follows:

[0008] Step 1: The zinc sulfate solution containing chlorine is neutralized and hydrolyzed to remove iron, and the precipitate and suspended matter is filtered to obtain a zinc sulfate solution containing chlorine with low iron content;

[0009] Step 2: The zinc sulfate solution containing chlorine in Step 1 is pumped into a container with a gas distribution plate at the bottom, a sealed cover at the top, and a gas guide pipe and valve installed; ozone or ozone air is continuously introduced from the bottom of the container at normal temperature and pressure, passes through the gas distribution plate and enters the solution for dechlorination; a zinc sulfate solution without chlorine is obtained for zinc production and mixed waste gas containing chlorine and oxygen;

[0010] Step 3: The chlorine-containing oxygen waste gas in Step 2 is subjected to two or more stages of absorption washing: the first stage of absorption washing liquid is saturated lime water solution or 5-15% sodium hydroxide solution; the second stage of absorption washing liquid is saturated lime water mixed with 5% sodium hydroxide solution or clean water, and the absorption washing of waste gas is carried out until it meets the standard for discharge; the first stage of absorption washing liquid is concentrated and crystallized to obtain calcium hypochlorite or sodium hypochlorite chemical products or is directly used as a disinfecting and deodorizing oxidizing agent for production or wastewater; the calcium hypochlorite or sodium hypochlorite crystallization mother liquor is returned to the lime water or lye for use.

[0011] Further, the zinc sulfate solution containing chlorine in Step 1 contains at least 1 g / L of chloride ions and 50-150 g / L of zinc; the neutralized and hydrolyzed iron removal solution has a pH of 4.5-5.5 and an iron content of less than 200 mg / L.

[0012] Further, the ozone or ozone air in Step 2 is generated by a dielectric barrier discharge method or an ozone generator, and the ozone content is 5-20%.

[0013] Further, the gas flow rate into the solution in Step 2 is 5-50 m 3 / min; the bottom of the container is double or triple, and the upper two layers are gas distribution plates; the terminal point of the gas oxidation and dechlorination is that the solution contains ≤100 mg / L of chloride ions.

[0014] Further, the waste gas discharge rate in Step 2 is 3-50 m 3 / min, controlled by the gas guide pipe valve, and the dechlorination process is in a slightly positive pressure state, the normal temperature is the natural temperature of the pumped solution and the terminal temperature of the gas oxidation, and the normal pressure is the natural pressure of the container generated between the control of the gas and the discharge of the waste gas.

[0015] Further, the saturated lime water in Step 3 is a calcium hydroxide aqueous solution obtained by soaking slaked lime for a long time and filtering; the lime water and sodium hydroxide mixed solution is a saturated lime water solution containing 5% sodium hydroxide.

[0016] Further, the other absorption washing liquid for the waste gas in Step 3 is clean water or weak acid water with a pH of 3-6.

[0017] The working principle of the present application:

[0018] The molecular formula of ozone is O3, and it has a V-shaped structure. At normal temperature and pressure, one oxygen molecule and an oxygen atom are decomposed from ozone. In aqueous solution, ozone is more easily decomposed with the increase of pH value and temperature. The decomposed oxygen atom has extremely strong oxidizing property, and its oxidation-reduction potential is only second to fluorine. The following table is the potential of commonly used oxidizing agents in aqueous solution.

[0019]

[0020] The decomposed oxygen atom of ozone can also decompose water molecules to obtain OH * (hydroxyl radical) intermediate transition state particles, which also have strong oxidizing property. Therefore, ozone can sufficiently oxidize chloride ions in aqueous solution into chlorine molecules to escape. The chemical reaction equation is as follows:

[0021] O3→O2+O, 2O+2Cl - →O2+Cl2

[0022] O+H2O→2OH * , 4OH * +2Cl - →Cl2+2H2O+O2

[0023] Chloride ions in the zinc sulfate solution containing chlorine exist in the form of hydrochloric acid, i.e. HCl→Cl - +H + , when the pH value is above 4.5, they mainly exist in the form of zinc chloride or ZnCl4 2- , i.e. ZnCl2→Zn 2+ +2Cl - , or

[0024]

[0025] Therefore, with the increase of pH value, the dechlorination efficiency of ozone in the zinc sulfate solution is greatly improved. The present application requires that the zinc sulfate solution containing chlorine has a pH value of 4.5-5.5. In addition to neutralizing and hydrolyzing the precipitated iron to remove the interference of iron ions, the main purpose is to make the chloride ions in the solution exist in the form of zinc chloride or ZnCl4 2- as much as possible to improve the oxidation efficiency of chloride ions. Further increasing the pH value will cause the hydrolysis loss of zinc ions.

[0026] The present application also uses a container device with double or triple layer structure at the bottom and sealed with a cover at the top in order to improve the efficiency of ozone oxidation and chlorine removal in aqueous solution. That is, a double or triple layer of gas distribution disc is arranged at the bottom to evenly distribute the ozone air entering from the bottom into the solution through the gas distribution disc, fully stir and contact the solution, and minimize dead angles and empty stops. The top is covered with a cover with a sampling hole and a waste gas outlet connected to the gas guide pipeline. The waste gas discharge rate is controlled by the valve of the gas guide pipeline to increase the gas pressure of the container and increase the oxidation and chlorine removal efficiency of ozone air. At the same time, the reaction waste gas is introduced into saturated lime water or sodium hydroxide solution for absorption and washing to comprehensively recover calcium hypochlorite or sodium hypochlorite. Through the above measures and working principle, the oxidation and chlorine removal effect of zinc sulfate solution containing chlorine can be greatly improved, and environmental pollution and production cost can be reduced.

[0027] The second feature of the present application is to use saturated lime water or sodium hydroxide solution or mixed solution of lime water and sodium hydroxide to absorb and wash the waste gas containing chlorine and oxygen, and as much as possible to generate calcium (sodium) hypochlorite for waste gas dechlorination discharge and comprehensive recovery.

[0028] When the chlorine-containing oxygen waste gas is washed with saturated lime water or 5-15% sodium hydroxide solution, the following chemical reactions will occur:

[0029] Ca(OH)2+Cl2+O→Ca(ClO)2+H2O (1)

[0030] 2 Ca(OH)2+2Cl2→Ca(ClO)2+CaCl2+2H2O (2)

[0031] 2NaOH+Cl2→NaClO+NaCl+H2O (3)

[0032] 2 Ca(OH)2+2NaOH+3Cl2→Ca(ClO)2+CaCl2+2NaCl+2H2O (4)

[0033] 2 Ca(OH)2+2NaOH+3Cl2+O→2Ca(ClO)2+2NaCl+3H2O (5)

[0034] Since the discharged waste gas is a multi-component mixed gas containing chlorine, oxygen, ozone, water vapor, etc., oxygen and oxygen atoms are generated by ozone decomposition, so the saturated lime water absorption and washing will mainly occur (1) chemical reaction to generate calcium hypochlorite and water. Avoiding the generation of calcium chloride to affect the crystallization quality of calcium hypochlorite or direct use effect. From the perspective of comprehensive recovery of useful chemical products, the waste gas of the present application is absorbed and washed by saturated lime water, which is better than sodium hydroxide solution absorption and washing, and also better than mixed absorption and washing liquid of lime water and sodium hydroxide. DETAILED DESCRIPTION

[0035] The application is further illustrated by the following examples.

[0036] A method for removing chlorine from a zinc sulfate solution containing chlorine by using ozone or ozone air, the specific implementation steps are as follows:

[0037] Step 1: First, the zinc sulfate solution containing chlorine is neutralized and hydrolyzed to remove iron, the pH of the zinc sulfate solution containing chlorine is 4.5-5.5, and the depth of iron removal is that the iron content in the solution after iron removal is ≤200 mg / L; then, the iron precipitate and other solid suspensions are filtered;

[0038] Step 2: The iron-removed solution of step 1 is pumped into a container provided with a gas distribution plate at the bottom, a cover at the top, and a gas guide pipeline and a valve control, and ozone or ozone air is continuously introduced from the bottom of the container to remove chlorine by oxidation under normal temperature and pressure;

[0039] The bottom of the chlorine removal container is a double-layer or triple-layer structure, and the upper part of the interlayer is one or two layers of gas distribution plates; ozone air enters from the bottom, passes through the gas distribution plates to enter the solution as evenly as possible, and forms uniform gas stirring; the upper part of the container is sealed with a cover, and the cover is connected to a gas guide pipeline through a sampling hole and a waste gas exhaust port, and is provided with a valve control to adjust the flow rate and pressure of ozone air in the container;

[0040] The ozone air is ozone air with an ozone concentration of 5-20% generated by a dielectric barrier discharge or other ozone generator;

[0041] The normal temperature refers to the natural temperature of the pumped zinc sulfate solution containing chlorine, and there is no heating and cooling device in the container;

[0042] The normal pressure refers to that the ozone air is introduced at a flow rate of 5-50 m 3 / min and the waste gas is discharged at a flow rate of 3-50 m 3 / min, forming a natural gas pressure; the obtained chlorine-removed zinc sulfate solution contains ≤100 mg / L of chloride ions, which is used for zinc metal production or zinc sulfate production, and the discharged waste gas is a mixed waste gas containing chlorine and oxygen;

[0043] Step 3: The chlorine-oxygen mixed waste gas of step 2 is washed by absorption in two or more stages to meet the emission standard, the first-stage absorption washing liquid is saturated lime water solution or 5-15% sodium hydroxide solution; the second-stage and above absorption washing liquid is a mixed solution of saturated lime water and 5% sodium hydroxide or clean water; the clean water is acidic water with a pH of 3-6; the waste gas is absorbed and washed until the waste gas meets the emission standard; when the first-stage absorption washing liquid contains calcium hypochlorite or sodium hypochlorite of more than 15%, it can be concentrated and crystallized or directly used for oxidation, disinfection, deodorization, and other processes or wastewater treatment, and the crystallization mother liquor is returned to the lime water or alkali water for use; the second-stage and above absorption washing liquid is returned to the first-stage absorption washing liquid for use.

[0044] Example 1: A zinc sulfate solution containing chloride ion 3.15 g / L, zinc ion 114 g / L, iron ion 1.2 g / L, As ion 0.5 g / L, Sb ion 0.3 g / L, Ni ion 0.8 g / L, Co ion 0.05 g / L, and PH = 2.5 was obtained from a certain enterprise. First, the iron was removed by neutralization and oxidation hydrolysis to obtain a solution with temperature 42°C, PH = 4.8, iron ion 0.12 g / L, As ion 0.02 g / L, Sb ion 0.01 g / L, Ni ion 0.06 g / L, Co ion 0.02 g / L, zinc ion 105 g / L, and chloride ion 3.32 g / L. Then, 50 L of the solution was taken and placed in a plastic container for ozone dechlorination test. The bottom of the plastic container was double-layered, the upper layer was a gas distribution plate, and the top was sealed with a cover having a sampling hole and an exhaust port. The exhaust port was tightly connected to an exhaust duct, and a valve was installed on the duct to control the flow rate. 10% ozone-containing air was continuously introduced from the bottom of the container at a rate of 10 m 3 / min, and the reaction exhaust gas was discharged from the top exhaust duct at a rate of 5-8 m 3 / min to maintain a slight positive pressure in the container. The exhaust gas was washed with saturated lime water at room temperature. The solution was sampled and analyzed every 15 min after ozone air was introduced, and the test was conducted for 60 min. The test results are as follows:

[0045]

[0046] The test results show that the ozone dechlorination effect is obvious, and the decrease in PH is caused by the hydrolysis of ferrous ion oxidized by ozone to form ferric ion and release acid. The increase in zinc ion is the result of water evaporation.

[0047] The reaction exhaust gas was washed with saturated lime water at room temperature, and after two-stage washing, the chlorine content in the exhaust gas was less than 0.1%.

[0048] Example 2: A zinc oxide raw material containing 3.5% chlorine and 45% zinc was leached with sulfuric acid to obtain a zinc sulfate solution containing 11.5 g / L chlorine, 122 g / L zinc, and 0.85 g / L iron. After neutralization and oxidation hydrolysis to remove iron, the solution contained 12.3 g / L chlorine, 118 g / L zinc, and 0.082 g / L iron. A 60 min ozone dechlorination test was conducted in the container equipment of Example 1 using 15% ozone-containing air. At the end of the test, the dechlorinated zinc sulfate solution contained 0.12 g / L chlorine, the reaction exhaust gas contained 5.2% ozone, and the exhaust gas was washed with 10% sodium hydroxide solution for three times. After washing, the chlorine content in the exhaust gas was 0.08%.

[0049] Example 3: The high-chlorine zinc sulfate leaching solution of Example 2 was treated with 15% ozone-containing air for dechlorination, and a total of 5 m 3The solution is recycled and washed by saturated lime water. Each cycle of absorption and washing is three stages. When the first stage absorption and washing solution contains calcium hypochlorite of more than 20 g / L, the solution is removed and concentrated to crystallize calcium hypochlorite. The second stage is upgraded to the first stage, the third stage is upgraded to the second stage, and new lime water is added to the third stage. This cycle is repeated for 5 m 3 After the solution is treated, the exhaust gas contains an average of 0.08-0.12 g / L of chlorine, and the quality of the obtained calcium hypochlorite crystals is more than 80%. The comprehensive recovery rate of chlorine reaches 82.5%.

[0050] Through the implementation of the above steps, the beneficial effect is to simplify the chlorine removal process of zinc sulfate solution containing chlorine, and to obtain zinc sulfate solution containing ≤100 mg / L of chlorine for electric zinc production or zinc sulfate heptahydrate production at low cost and high efficiency. At the same time, the chlorine obtained by removing chlorine is converted into calcium hypochlorite or sodium hypochlorite chemical products for sale or reuse as a disinfecting, oxidizing, deodorizing agent for other processes or wastewater treatment, achieving good social and economic benefits.

[0051] The above examples are only further illustrations of the present application, and the present application is not limited thereto.

Claims

1. A method for removing chlorine from a zinc sulfate solution containing chlorine using ozone or ozone air, characterized in that: The specific implementation steps are as follows: Step 1: Neutralize, hydrolyze, purify, and remove iron from the zinc sulfate solution containing chlorine, and filter out the precipitate and suspended solids to obtain a zinc sulfate solution containing chlorine with low iron content; Step 2: Pump the chlorinated zinc sulfate solution from Step 1 into a container equipped with a gas distribution plate at the bottom, a sealed cap at the top, and gas delivery pipes and valves; continuously introduce ozone or ozone air from the bottom of the container at room temperature and pressure, which then enters the solution through the gas distribution plate for dechlorination; obtain a dechlorinated zinc sulfate solution for use in zinc production and as a mixed waste gas containing chlorine and oxygen. Step 3: The chlorine-containing waste gas from Step 2 is subjected to two or more stages of absorption and washing: the first stage absorption and washing liquid is a saturated lime water solution or a sodium hydroxide solution containing 5-15% sodium hydroxide; the second stage absorption and washing liquid is a mixed solution of saturated lime water and 5% sodium hydroxide or clean water. The waste gas is absorbed and washed until it meets the emission standards. The first-stage absorption washing liquid is concentrated and crystallized to obtain calcium hypochlorite or sodium hypochlorite chemical products, or it can be used directly as a disinfectant, deodorizing, and oxidizing agent for production or wastewater; the mother liquor of calcium hypochlorite or sodium hypochlorite crystallization is returned to be used to prepare lime water or alkaline water; The zinc sulfate solution containing chloride ions in step 1 contains at least 1 g / L of chloride ions and 50-150 g / L of zinc; the neutralized hydrolysis purified iron removal solution has a pH of 4.5-5.5 and an iron content of less than 200 mg / L. The ozone or ozone air in step 2 is generated by dielectric barrier discharge or an ozone generator, and contains 5-20% ozone. The aeration rate to the solution in step 2 is 5-50 m³ / min; the bottom of the container is double or triple-layered, with the top two layers being gas distribution plates; the endpoint of aeration oxidation and dechlorination is when the chloride ion content in the solution is ≤100 mg / L. The exhaust gas discharge rate in step 2 is 3-50 m³ / min, controlled by the valve in the gas delivery pipeline. The dechlorination process is under a slight positive pressure. The ambient temperature is the natural temperature of the pumped solution and the end temperature of the gas oxidation. The ambient pressure is the natural pressure of the container between the gas supply and the exhaust gas discharge. The saturated lime water in step 3 is a calcium hydroxide aqueous solution that has been soaked in quicklime for a long time and then filtered. In step 3, the first-stage absorption washing liquid containing calcium hypochlorite or sodium hypochlorite of 15% or more can be removed for concentration and crystallization, and directly used as an oxidant in production and other wastewater treatment, depending on production needs.

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