Leaching of Zinc for Subsequent Recovery by Hydrometallurgical Techniques from Electric Arc Furnace Dusts and Utilisation of the Leaching Process Residues for Ceramic Materials for Construction Purposes

Steel is one of the most widely used materials in the past and today. Various techniques are used to recycle this material, including the electric arc furnace. This process has several advantages, but it also has a major disadvantage, namely, the generation of waste such as electric arc furnace dusts. Electric arc furnace dusts are classified as hazardous waste due to their high percentage of heavy metals, including zinc. Consequently, in the present research, the leaching of zinc for recovery with sulfuric acid solutions at ambient temperature and atmospheric pressure is evaluated, as well as the reuse of the leaching process residue as a raw material for ceramic materials. The sulfuric acid solutions were 0.125, 0.25, 0.5, and 1 molar, using clay for ceramic conforming and percentages of the leaching residue from 0–50%. The results showed that the optimum solution was 1 molar sulfuric acid, recovering all the zinc in the sample in 36 h. Furthermore, it was found that the clay-conformed ceramics with less than 40% leaching residue showed acceptable physical and mechanical properties according to standards. Therefore, this research develops a new environmental hydrometallurgy in which metallic elements of interest are valorized and the production of waste is avoided, reducing the deposition of hazardous waste in landfills and the extraction of raw materials for the manufacture of construction materials.

Preparation of Zinc Oxide and Zinc Ferrite from Zinc Hypoxide by Wet Process and Electrochemistry

With the increase of zinc resource consumption, the recovery and utilization of zinc resources in zinc suboxide has become one of the current research hotspots. In this study, the electrochemical method was used to remove the impurities in the zinc leaching night and enrich the zinc ferrite in the ammonia leaching residue for the solution and ammonia leaching slag after the ammonia leaching of zinc hypoxide, in order to realize the comprehensive utilization of the essence of zinc immersion night and new resources. The results showed that the reduction potentials of copper, lead, cadmium, and zinc in the ammonia leaching solution were analyzed by electrochemical testing methods to be −0.76 V, −0.82 V, −0.94 V, and −1.3 V, respectively. Through constant potential electrodeposition, the removal rate of copper, lead, cadmium. The removal rate of cadmium is 98.73%, and the removal rate of lead and copper is more than 99%. The purified ammonia leaching solution is evaporated at 90 °C for 25 min to obtain basic zinc carbonate. The purity of ZnO obtained after calcination at 500 °C for 120 min is 96.31%. The ammonia leaching residue was pickled with 3 mol·L−1 acetic acid for 30 min to effectively remove PbCO3, and then magnetic separation was carried out with a current intensity of 1.4 A. The final zinc ferrite content was 83.83%.

Adaptive process for improving leaching efficiency of germanium from secondary zinc oxide

Adaptive process was used to treat germanium-containing secondary zinc oxide. The leaching parameters were determined by batch experiment, and continuous experiment was conducted and the stability of the process was verified. The leaching efficiency of Zn and Ge in the batch experiments were 92.51 and 90.67%, respectively, while the leaching efficiencies of Zn and Ge in the continuous experiment were 93.53 and 88.47%, respectively. In the neutralization process, the Fe3+ concentration in the neutralized solution is within 0.025 g/L. The Fe2+in the leaching solution increased gradually, as the neutralized residue was returned to the leaching process, the Zn in leaching residue reduce and the leaching efficiency of Zn increased. The residue mainly contained zinc sulfide and lead sulfate, with some fluffy structures on the surface. The process is promising for industrial application from indicators, economy, and applicability.

Understanding the behaviour of zinc and impurities during alkaline leaching of zinc bearing product obtained as a result of pyrometallurgical processing of ferrous metallurgy dusts and examining the phase composition of leaching residue

This paper describes a technique developed for processing EAF dusts and recovering zinc. The technique is based on the Waelz process without zinc sublimation and allows to obtain a product suitable for hydrometallurgical processing and clear of lead or halogens in one process stage. It would be feasible to use an alkaline hydrometallurgical process for this product as it enables a selective recovery of zinc while iron remains in the solid residue. A pyrometallurgical process is necessary to remove halogens, increase the solubility of zinc and remove lead. In the alkaline process, the latter transfers to the solution together with zinc. As part of the development procedure, the thermodynamics of lead and iron in alkaline medium was studied. For this, equilibrium diagrams were built in the Eh – рН coordinates. Findings: – zinc can dissolve at рН > 12.7 while forming the following anions: ZnO22– and [Zn(OH)n]2–n. A study that looked at leaching zinc ores confirms that anions of the latter type do form; – lead can dissolve while forming [Pb(ОН)6]2–-type hydroxo complexes at рН > 12.5. When the solution is heated to 80 oС, their solubility can reach 140 g/dm3. In a hot solution hydroxo complexes form orthoplumbite and orthoplumbate ions PbО22–, PbО32– as a result of dehydration; – the low solubility of all iron compounds in alkaline medium and their position in the diagram only defined by the pH range suggest that the leach solutions contain no iron ions of any type. With the temperature raised to 80 oС, the equilibria in the Fe – H2O system remains unchanged in alkaline medium and no significant increase in the solubility of iron compounds is observed. The findings show that selective dissolution of products containing zinc oxides (including EAF dusts after the above mentioned pyrometallurgical process) in alkaline solutions is feasible. The zinc leaching residue was analyzed for chemical and phase composition to find possible applications for it. It is demonstrated that calcium ferrites, aluminates and alumosilicates account for 80% of the residue. This iron-calcium material can be utilized by cement industry.

A Combined Soda Sintering and Microwave Reductive Roasting Process of Bauxite Residue for Iron Recovery

In this study an integrated process is presented as a suitable method to transform Fe3+ oxides present in bauxite residue into magnetic oxides and metallic iron through a microwave roasting reduction, avoiding the formation of hercynite (FeAl2O4). In the first step, all the alumina phases were transformed into sodium aluminates by adding sodium carbonate as a flux to BR and then leached out through alkali-leaching to recover alumina. Subsequently, the leaching residue was mixed with carbon and roasted by using a microwave furnace at the optimum conditions. The iron oxide present in the sinter was converted into metallic iron (98%). In addition, hercynite was not detected. The produced cinder was subjected to a wet high intensity magnetic separation process to separate iron from the other elements.

Selective Flotation of Elemental Sulfur from Pressure Acid Leaching Residue of Zinc Sulfide

An efficient flotation process was developed to selectively recover elemental sulfur from a high-sulfur pressure acid leaching residue of zinc sulfide concentrate. The process mineralogy analysis showed that the sulfur content reached 46.21%, and 81.97% of the sulfur existed as elemental sulfur which was the major mineral in the residue and primarily existed as pellet aggregate and biconical euhedral crystal. An elemental sulfur concentrate product with 99.9% of recovery and 83.46% of purity was obtained using the flotation process of one-time blank rougher, two-time agent-added roughers, and two-time cleaners with Z-200 as collector and Na2S + ZnSO4 + Na2SO3 as depressant. The flotation experiment using return water indicated that the cycle use of return water had no adverse effect on the flotation performance of elemental sulfur. The process mineralogy analysis manifested that main minerals in the residue directionally went into the flotation products. Most of elemental sulfur entered the concentrate while other minerals almost completely went into the tailing. Main valuable elements lead, zinc, and silver entered the tailing with sulfides and could be recovered by lead smelting. The proposed process can realize the comprehensive recovery of valuable components in the high-sulfur residue and thus it has wide industrial application prospect.