Jorge M.R. Carvalho

Iron recovery from sulphate leach liquors in zinc hydrometallurgy

Abstract Iron is usually present in leach solutions and its elimination is a major operational problem in zinc hydrometallurgy. The recovery of iron from such solutions is usually carried out by precipitation as jarosite, goethite or hematite. These residues, contaminated with heavy metals ions such as Zn, Pb, In, Ga, Ge, Co and sulphur, are environmentally unacceptable and their disposal in controlled ponds is very expensive. This fact justifies the interest in producing iron as a marketable product––pure hematite. With this purpose solvent extraction is being investigated as a promising alternative for the recovery of iron from leach solutions.

Recovery of 2-chlorophenol from aqueous solutions by emulsion liquid membranes: batch experimental studies and modelling

Abstract A study of 2-chlorophenol recovery by emulsion liquid membranes was undergone. The effect of several permeation variables such as membrane phase composition, internal reagent concentration, solute concentration, permeation stirring speed, temperature, permeation time and phase ratios between membrane phase and internal phase and also between external phase and internal phase on 2-chlorophenol permeation was studied. The most relevant of these parameters were permeation stirring speed, temperature and phase ratio between external phase and internal phase. Advancing front model was applied to these parameters and described the experimental results.

A comparison of models for 2-chlorophenol recovery from aqueous solutions by emulsion liquid membranes

Advancing front model and three reversible reaction models were applied to describe 2-chlorophenol permeation from aqueous solutions by emulsion liquid membranes. Similar results were obtained in most cases by using either of the reversible reaction models. Also differences between reversible reaction and the advancing front model were shown to be within experimental error in most cases (with the exception of low temperature permeation data) meaning that the role of reversibility of the chemical reaction between internal phase reagent and 2-chlorophenol can be considered negligible. Both advancing front and reversible reaction models can be used with a reasonably accuracy as estimates of 2-chlorophenol permeation for design purposes.

Copper extraction from ammoniacal medium in a pulsed sieve-plate column with LIX 84-I

This article reports on a study of copper removal from ammoniacal aqueous solution (1.0 kg m(-3) Cu, pH 9.5) by liquid-liquid extraction using a pulsed sieve-plate column. The extractant tested was the hydroxyoxime LIX 84-I (2-hydroxy-5-nonylacetophenone oxime) in the aliphatic diluent Shellsol D-70. The results of the pilot plant experiments demonstrated the feasibility of operating the extraction process in this type of column, with efficiencies of copper removal in the range of 90.5-99.5%. Several effects on the column performance were examined, namely the aqueous and organic flow rates and the pulse velocity. The axial dispersion model was applied to simulate the concentration profiles, which reasonably predicted the experimental data. The overall mass transfer coefficient was evaluated from the experimental data and was found to be between 9×10(-6) and 1.2×10(-5) m s(-1). These data were compared with the ones obtained from the resistances in series model, which indicated that the resistance due to chemical reaction was 84-91% of the overall resistance to mass transfer. The extraction using a hollow fiber contactor was also carried out to compare the membrane process performance with the one of conventional process.

Extraction Equilibrium of Copper from Ammoniacal Media with LIX 54

Abstract This paper reports a study of the extraction of copper from ammonia/ammonium sulfate medium with LIX 54, a β‐diketone. The extraction of copper is very sensitive to the equilibrium pH. The highest extraction efficiency is attained in the range of pH 8–9.5. Above pH 10, the percentage of metal ion extracted decreases sharply. The extraction of copper by LIX 54 can be described by the following equation: The thermodynamic equilibrium constant was evaluated in terms of the aqueous phase and was found to be 10(2.89±0.03) M2 at 298 K. The nonideality of the aqueous phase was taken into account by applying the Pitzer model and the extended Debye‐Hückel equation. The isotherms of extraction for the system copper/ammonia/ammonium sulfate/LIX 54 revealed that the increase in the salt concentration from 0.2 to 1 M makes the extraction process difficult.

The leaching of tetrahedrite in ferric chloride solutions

Abstract This paper presents a study of the kinetics of the leaching of tetrahedrite in FeCl3–NaCl–HCl solutions for temperatures between 60°C and 104°C and ferric ion concentrations of 0.001 to 1 M at atmospheric pressure. The shrinking core model was applied to the results. The calculated activation energy is 65±6 kJ/mol; the order of the reaction with respect to ferric ion is 0.35±0.03; and the apparent rate constant is proportional to the inverse of the mean particle size. These results show that, for temperatures below the normal boiling point of the solution, the leaching of tetrahedrite is reaction controlled. From the analyses of the solutions and X-ray and microprobe analyses of the solid residues, it was concluded that the leaching of tetrahedrite involves the complete breakdown of the sulphide structure.

Review on the Recent Developments in the Solvent Extraction of Zinc

Solvent extraction (SX) of zinc is useful for the recovery of high purity zinc from the leaching solutions of its sulphide minerals, several low‐grade ores, and secondary materials. The technique is fast, environmentally sustainable, and can be tailored to treat aqueous solutions of diverse compositions. It is particularly useful in the cases where the level of contamination is high and the upgrading of the desired metal is necessary. The present paper reviews the use of several acidic, basic, and solvating extractants for the recovery of zinc from different acidic media. The important aspects of the extraction processes have been discussed and some of the noteworthy applications of the SX in the treatment of ores and secondary materials are presented.

Salt Effects on the Recovery of Phenol by Liquid‐Liquid Extraction with Cyanex 923

Abstract In this work, the effect of salt addition on the recovery of phenol from a 46 g/L aqueous solution simulating a phenolic resin plant effluent by liquid‐liquid extraction at 298 K has been studied by using an organic phase containing 0.6 M Cyanex 923 extractant in ShellSol T. Addition of sodium sulfate, potassium nitrate, and sodium chloride to the aqueous phase was tested and sodium chloride was selected. Based on the obtained results, a study of phenol recovery process was undergone by taking advantage of the salting‐out effect. Equilibrium curves are presented for liquid‐liquid extraction with and without salt addition to the aqueous phase. An integrated process involving salting‐out and liquid‐liquid extraction was proposed. The stripping concentrates can be reused for phenolic resin production.

Study of the autoclave leaching of a tetrahedrite concentrate

Abstract Tetrahedrite is a sulphide of copper and antimony with the general chemical formulae Cu 12 Sb 4 S 13 . It is very difficult to find pure natural tetrahedrite because its original constituents are always partially substituted by other elements. Thus, arsenic can substitute for antimony leading to tenantite (Cu 12 As 4 S 13 ), while copper can be substituted by zinc, silver, mercury, iron, cadmium etc. This work describes the purification of an impure tetrahedrite/tenantite concentrate and presents the results obtained in some pressure leaching tests of the as-received or partially purified concentrate. The results show that, after two purification steps, it was possible to obtain a concentrate with 90 % tetrahedrite/tenantite and, under certain conditions, it was possible to leach 70 % of the copper and 85 % of the silver and zinc contained in the concentrate.

Leaching of gold from a Portuguese concentrate with thiourea

Abstract A Portuguese gold concentrate constituted mainly of arsenopyrite was leached with thiourea in sulphuric acid medium. two sets of experiments were carried out to determine the effect of some variables on gold extraction. The variables studied were: thiourea concentration, the concentration and type of the oxidizing agent, pulp density and temperature.