The sludge from a wet-off gas cleaning system of the iron blast furnace (BF) contains significant amounts of iron; however, they cannot be recycled due to their high content of zinc and alkalis. These compounds are detrimental to the optimal performance of iron and steelmaking furnaces. In this work, a comparative laboratory study to reduce zinc and alkali contained in the blast furnace sludge (BFS) is presented. The effect of leaching parameters such as oxidant (i.e., ferric ion, oxygen or ozone), aqueous solution media (i.e., 0.2 M NH4Cl, 0.2 M HCl and 0.1 M H2SO4) and temperature (i.e., 27 and 80 °C) on Zn and alkalis (Na2O and K2O) removal were studied by applying an experimental design. The results obtained show that Zn and K2O removal of 85% and 75% were achieved under the following conditions: Ozone as an oxidant agent and 0.1 M H2SO4 as an aqueous medium, temperature had no significant effect. The results are supported by thermodynamic diagrams and the possible chemical reactions are mentioned. Although the results also indicate that leaching under the above conditions dissolves up to 9% of iron, this loss is much less than leaching without the oxidizing conditions generated by the ozone. The BFS obtained from this treatment could be recirculated to the iron or steelmaking processes to recover iron values.

This work examines the role of NaOH and Ca(OH) 2 on the hydrothermal decomposition of industrial jarosite deposited by a Mexican company in a tailings dam. The industrial jarosite is mainly composed by natrojarosite and contains 150 g Ag/t, showing a narrow particle size distribution, as revealed by XRD, fire assay, SEM-EDS and laser-diffraction analysis. The effect of the pH, when using NaOH or Ca(OH) 2 as alkalinizing agent was studied by carrying out decomposition experiments at different pH values and 60°C in a homogeneous size particle system (pH = 8, 9, 10 and 11) and in a heterogeneous size particle system (pH = 11). Also, the kinetic study of the process and the controlling step of the decomposition reaction when NaOH and Ca(OH) 2 are used was determined by fitting the data obtained to the shrinking core model for spherical particles of constant size. These results, supported by chemical (EDS), morphological (SEM) and mapping of elements (EDS) analysis of a partially reacted jarosite particle allowed to conclude that when NaOH is used, the process kinetics is controlled by the chemical reaction and when Ca(OH) 2 is used, the rate determining step is changed to a diffusion control through a layer of solid products.

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Electronic waste (e‐waste) contains metallic values that can be recovered by hydrometallurgical methods. This investigation addresses the leaching kinetics of e‐waste for the recovery of copper in H2SO4‐H2O2 media with the objective of determining the rate‐controlling step in monosize particle systems. The results are then used to develop a kinetic model for copper dissolution in multisize particle systems. It is shown that in a monosize particle system, Cu dissolves completely in 150 min at 2 M H2SO4 and 0.2 M H2O2. The rate‐controlling step for this process is chemical reaction with an activation energy of 47.8 kJ/mol. The kinetic model for Cu dissolution in multisize particle systems is developed by applying an optimization method that considers the size distribution and the copper content of each of the size fractions. The results show that the model predicts satisfactorily the Cu dissolution kinetics and reveals that Cu particles with mean sizes of 79, 141, 237, 398.5, and 605 μm react completely in times varying from 15 to 120 min. Coarser Cu particles do not react completely in a time interval of up to 120 min. E‐waste losses 57.6% of its initial weight when subjected to the leaching process and solid residue has gold and silver grades of 2 402.35 and 9 035.29 g/ton, respectively.