Innovative methodology for comprehensive utilization of high iron bearing zinc calcine

Technical and Economic Comparison between Sodium and Ammonium Agents in the Jarosite Precipitation Process-An Evaluation for Industrial Applications

Iron content can cause severe challenges through zinc production from zinc sulfide concentrate. The zinc industry extensively uses the jarosite precipitation process (JPP) to precipitate dissolved iron and remove it before transferring the solution to downstream stages. Precipitating agents (PAs) play an essential role in the JPP. However, surprisingly, no study compares the efficiency of various PAs on an industrial scale. As an innovative approach, this investigation compares the technical and economic aspects of using various sodium and ammonium compounds (hydroxides, carbonates, bicarbonates, sulfates, and bisulfates) as typical PAs for the JPP at the Bafgh Zinc Smelting Company (BZSC) plant. Experimental results revealed that ammonium hydroxide, with 90.85% iron removal efficiency, had the highest performance, and sodium bisulfate and ammonium bisulfate had the lowest efficiency (74.54 and 77.13%, respectively). However, since ammonium hydroxide is a corrosive PA, it is not a promising alternative to sodium sulfate (with both economic and safety issues). Based on technical and economic assessments, sodium carbonate (84.31% iron removal efficiency) showed the highest potential for an efficient JPP.

A clean process for phosphorus recovery and gallium enrichment from phosphorus flue dust by sodium carbonate roasting

Phosphorus flue dust (PFD) is a solid waste product from phosphorus (P) production that contains P and is enriched with gallium (Ga). The recovery of these valuable components not only protects the environment, but also reduces resource waste. This study aimed to develop a green and efficient method to recover P and enriched Ga from PFD. The effects of different parameters on the P leaching rate and Ga loss rate during Na₂CO₃ roasting and water leaching were investigated and optimized. The reaction mechanisms during the experiment were characterized, revealing that the P-containing compounds in PFD mainly transformed into water-soluble Na₃PO₄. Furthermore, the leaching rate of P reached 85.38%, while Ga was mainly concentrated in the residue and its loss rate was only about 1%. Ga content in the residue reached about 0.1%. An attempt was made to recover Na⁺ and PO₄^3- from the aqueous solution by evaporative crystallization and XRD analysis showed that the main phase of the crystallization product was Na₂HPO₄. The proposed process is technically simple, only Na₂CO₃ is added and no hazardous substances are generated, and represents a new method for recovering P and enriching Ga from PFD.

Effect of Lead and Zinc Impurities in Ironmaking and the Corresponding Removal Methods: A Review

This paper reviews the effects of Pb and Zn impurities and their removal in the ironmaking process. The phase changes during ironmaking were investigated, along with the removal techniques of such impurities and their environmental impact. Results show that distribution of Pb–Zn–Fe in Fe ore is complicated, the particles are fine, and the removal of mineral phase at high temperature is difficult. Therefore, the production and occurrence of Pb and Zn impurities in the ironmaking process were analyzed; such impurities reduced the overall productivity of the process. In addition, the important treatments for the removal of these impurities were investigated. Most of these processes eliminated the Pb and Zn impurities from the dust or sludge, but the main impact of the reduced productivity of the ironmaking process in the furnaces was still observed.

Selective Separation of Arsenic from Lead Smelter Flue Dust by Alkaline Pressure Oxidative Leaching

This study investigated the feasibility of using an alkaline pressure oxidative leaching process to treat lead smelter flue dust containing extremely high levels of arsenic with the aim of achieving the selective separation of arsenic. The effects of different parameters including NaOH concentration, oxygen partial pressure, liquid-to-solid ratio, temperature, and time for the extraction of arsenic were investigated based on thermodynamic calculation. The results indicated that the leaching efficiency of arsenic reached 95.6% under the optimized leaching conditions: 80 g/L of NaOH concentration, 1.0 MPa of oxygen partial pressure, 8 mL/g of liquid-to-solid ratio, 120 °C of temperature, 2.0 h of time. Meanwhile, the leaching efficiencies of antimony, cadmium, indium and lead were less than 4.0%, basically achieving the selective separation of arsenic from lead smelter flue dust. More than 99.0% of arsenic was converted into calcium arsenate product and thus separated from the leach solution by a causticization process with CaO after other metal impurities were removed from the solution with the addition of Na2S. The optimized causticization conditions were established as: 4.0 of the mole ratio of calcium to arsenic, temperature of 80 °C, reaction time of 2.0 h. The resulting product of calcium arsenate may be used for producing metallic arsenic.

Preparation of Calcium Stannate from Lead Refining Dross by Roast–Leach–Precipitation Process

Lead refining dross containing plenty of tin and other heavy metals, such as lead and antimony, is considered a hazardous waste generated in large quantities in lead smelter plants. In this study, calcium stannate was synthesized from lead refining dross using sodium carbonate roasting and alkaline leaching followed by precipitation with CaO. The effect of roasting and leaching parameters on the extraction efficiency of tin was investigated. The leaching efficiency of tin reached 94% under the optimized conditions: roasting with 60% Na2CO3 at 1000 °C for 45 min, and leaching using 2 mol/L NaOH solution for 90 min at 85 °C and 8 cm3/g liquid/solid ratio. Furthermore, more than 99% of tin in the leaching solution was precipitated using CaO. Finally, XRD, SEM, and ICP-OES analyses indicated that the final CaSnO3 product had a purity of 95.75% and its average grain size was smaller than 5 μm. The results indicated that the developed method is feasible to produce calcium stannate from lead refining dross.

Sulfidation mechanism of ZnO roasted with pyrite

Sulfidation is a widely used technology to improve the floatability of oxidized metal minerals or to stabilize the heavy metals in various wastes. The sulfidation mechanism of ZnO with pyrite was detailedly studied by thermodynamic calculation and roasting experiments. The sulfidation behaviors, phase transformations, microscopic morphology and surface properties were investigated by TG-DSC, ICP, XRD, SEM-EDS, and XPS analysis. The results indicate that the nature of the sulfidation is the reaction of ZnO with the gaseous sulfur generated by the decomposition of pyrite. Pyrite instead of sulfur as the sulfidizing agent can not only relieve the volatilization loss of sulfur but also enhance the formation of liquid phase and thus facilitate the growth of ZnS particles. The sulfidation reaction belongs to surface chemical reaction and relates to the migration of oxygen from the inside of ZnO to its surfaces. The presence of carbon not only eliminates the release of SO₂, but also decreases the decomposition temperature of pyrite and promotes the sulfidation of ZnO. The addition of Na₂CO₃ promotes the sulfidation of ZnO at lower temperatures (below 850 °C) and enhances the growth of ZnS particles but has a negative effect on the sulfidation at higher temperatures.

Mechanism study on the sulfidation of ZnO with sulfur and iron oxide at high temperature

The mechanism of ZnO sulfidation with sulfur and iron oxide at high temperatures was studied. The thermodynamic analysis, sulfidation behavior of zinc, phase transformations, morphology changes, and surface properties were investigated by HSC 5.0 combined with FactSage 7.0, ICP, XRD, optical microscopy coupled with SEM-EDS, and XPS. The results indicate that increasing temperature and adding iron oxide can not only improve the sulfidation of ZnO but also promote the formation and growth of ZnS crystals. Fe₂O₃ captured the sulfur in the initial sulfidation process as iron sulfides, which then acted as the sulfurizing agent in the late period, thus reducing sulfur escape at high temperatures. The addition of carbon can not only enhance the sulfidation but increase sulfur utilization rate and eliminate the generation of SO₂. The surfaces of marmatite and synthetic zinc sulfides contain high oxygen due to oxidation and oxygen adsorption. Hydroxyl easily absorbs on the surface of iron-bearing zinc sulfide (Zn_1−xFe_xS). The oxidation of synthetic Zn_1−xFe_xS is easier than marmatite in air.