Recovery of zinc from electric arc furnace soot

May 06, 2024

1 Overview The use of wet and pyrometallurgical methods to recover DC EAF. DC EAF has many research results. The pyrometallurgical process requires a reducing agent and is heated to a high temperature to produce crude zinc oxide having a low industrial value; while a hydrometallurgical process can produce high-purity metallic zinc and zinc oxide, but cannot completely leach zinc from zinc ferrite.

The hot acid leaching method is very practical for treating zinc ferrite particles in DC EAF. For example, the sulfuric acid is cheap, and it is an effective reagent for leaching zinc in zinc ferrite at low temperature. The disadvantage is that when leaching under normal pressure, the jarosite can be produced at a pH of <2, and the toxic element PEAF cannot be leached. A few percent of the chloride must be removed prior to electrolysis to avoid attacking the anode material used in the sulfuric acid leaching system.

Hydrochloric acid has also been found to be a very effective leaching agent for leaching zinc ferrite from DC EAF soot. The zinc yield is high and does not produce jarosite. When 90~1002 is used, 0.5~1mol/L HCl can be used to extract about 90% of total Zn, and about 80% of total Fe is dissolved.

In the recycling process, the leaching and electrowinning steps must meet the requirements of 3 points: 1 All reagents should be recycled at a high rate and economically reused; 2 The product should be valuable, and the harmful residues should be as small as possible to save processing costs; The system should be safe, easy to operate, and not occupy a large space. The main advantage expected by the HCl leaching method is that the activity coefficient of HCl in an aqueous solution of 10.5~5mol/L does not decrease sharply with the increase of acid concentration and is different from H-SO%. 2 Chloride contained in soot Conducive to the leaching process; 3 no need to wash the soot for the removal of chloride; 4 soluble chloride can remove the toxic elements Pb and Cd from the soot; 5 can avoid the formation of jarosite; 6 in the chloride system by filtration Separating the solid to liquid ratio is easier in the sulfuric acid system; 7 the hydrochloric acid containing chloride solution has a higher conductivity than the sulfuric acid containing sulfate solution, which can lower the cell voltage.

One of the problems with HCl leaching-electrowinning is the production of Cl- instead of HCl during electrowinning. When recovering nickel, the possibility of directly regenerating HCl with a membrane electrolyzer was investigated and it was found that when a single -18-cation exchange was used In the membrane electrolyzer, the decrease in the pH of the catholyte results in a low cathode current benefit and a poor quality of the nickel deposit. When a double membrane electrolyzer is used, the pH of the catholyte is kept stable, and the chlorin concentration of the anolyte is small. This electrodialysis process can recover metals and hydrochloric acid, but is less used in industrial wastewater treatment because of the higher investment and operating costs from the perspective of zinc recovery. This article focuses on the study of zinc and HCl recovery using a single membrane electrolyzer.

2 Research Example 2.1 Method Overview A two-step method was designed to completely extract zinc from soot by the countercurrent leaching method of soot and leaching agent. As shown, the soot is leached twice: for the first time, the zinc oxide is leached from the soot; the second time, the hot hydrochloric acid solution is reacted with the zinc ferrite residue from the low acid leaching vessel. The iron in the hot acid leaching residue was found to be hematite Fe-O) and goethite FeO*OH). The hot acid leaching filtrate has a lower pH and contains more ferric chloride, which is used to leach fresh soot. The solution is filled with air or oxygen to remove iron from the filtrate, treated with zinc oxide and metal zinc powder to remove other elements of the filtrate by low acid leaching, or to simultaneously remove organic matter with activated carbon. The clean liquid is transferred into an electric storage tank having an ion exchange membrane to produce HCl and zinc.

Recovery of zinc from EAF soot by acid leaching and electrolysis 2.2 Test work 2.2.1 Characteristics of leaching leaching materials are shown in Table 1. Leaching was carried out in 700 ml of a reaction glass vessel equipped with a heat controller and a water-cooling device. The concentration of HCl is 0.5~2mol/L, the quantity is 500ml, and the soot is stirred between 25~902 to make it leaching. The pH of the acid leachate is 0.0 to 2. In order to eliminate iron, fresh soot is added together with a small amount of 29% H0 solution to adjust the pH to 4.0 to 5.0 to oxidize the ferrous iron. 100 g of soot was leached with a calculated amount of HC1.

Further, zinc powder was added to the filtrate produced by the dilute acid leaching to precipitate Pb, Cu and Cd. The reaction was completed in 10 minutes, and the pure filtrate was suitable for electrolytic production of high-purity zinc.

The residue precipitated after leaching and displacement was dissolved in hot aqua regia and analyzed by AAS.

Table 1 chemical composition of EAF soot, wt% sample 1 sample average particle size:! m specific surface area: m2 / g * BET zinc ferrite: wt% Zn / soot in zinc ferrite > zinc ferrite is not completely separated from magnetite.

Electrolysis was carried out in a rectangular electrolytic cell made of polycarbonate which was divided into two chambers by a cation exchange membrane. The exchange membrane was supported between two perforated 1 mm thick Teflon plates. The membrane area was 72 cm 2 and 18 cm 2 respectively. The electrode was 6 cm x 12 cm, but only 6 cm x 6 cm was directly exposed to the electrolyte, and the rest was covered with insulating varnish. The cathode is made of an industrial pure 99% aluminum plate polished with SiC paper, and the anode is a Pt titanium plate. The distance between the poles is 4.5 cm. The anode chamber is filled with 250 m11mo1/LH2S4, and the cathode chamber contains a 250 ml ZnCl2 solution. Air is blown in to inhibit the growth of dendrites from zinc deposits. The chloride concentration in the anolyte was determined using a chloride ion selective electrode. 1 ml of the sample solution was taken and diluted with distilled water to 100 ml. Before the chloride ion was measured with a chloride ion selective electrode, 2 ml of the ionic strength modifier 5mo1/LNaN03) was mixed with the dilute solution. The measured electrode potential is converted to a chloride concentration using standard calibration data. The chemical composition of the electrodeposited layer was determined by AAS and energy dispersive X-ray spectroscopy (EDS). The acidity of the catholyte was determined by titration with 0.5 mol1/L Na2C03 solution.

3 Test conclusion 3.1 When the zinc ferrite particles are dissolved in hydrochloric acid with a concentration of 1~2mol/L, the recovery of Zn is >90%. 3.2 In the solution of the acid molar ratio of 4.06.0, from the zinc ferrite Zinc is preferentially leached from the EAF soot. Iron is removed from the system with FeOOH and Fe23.

3.3 With dilute acid leaching, iron can be removed from the solution by means of oxidation.

3.4 EAF soot may contain organic complexes of metals, but can be removed with activated carbon without loss of Zn.

The degree increases and decreases.

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Author:

Mr. Ziyu Song

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