Richard Diaz Alorro

On the Use of Magnetite for Gold Recovery From Chloride Solution

The sorption of gold chloride ( ) from chloride solution on synthetic and natural magnetite powders was investigated by batch sorption experiments. The effects of different parameters on the recovery were studied. The results showed that Gold (Au) uptake by magnetite was influenced by pH, contact time, chloride concentration, and initial Au concentration. Gold uptake by synthetic and natural magnetite was maximum at pH 6–7 with sorption amounts of 4.4 μmol/g and 5.0 μmol/g, respectively, after 24 hr at an initial Au concentration of 0.05 mol/m3. The Scanning Electron Microscopy–Energy Dispersive X-ray and Back Scattering Electron analyses of the magnetite particles after treatment confirmed the presence of Au precipitates on the magnetite (Fe3O4) surface.

A Study on the Utilization of Magnetite for the Recovery of Platinum Group Metals from Chloride Solution

ABSTRACT The recovery of platinum group metals (PGMs) from chloride solution using magnetite was investigated. The adsorption of platinum, palladium, and rhodium in chloride medium onto synthetic magnetite powders were studied at different pH conditions, contact time, sodium chloride concentrations, and initial Pt, Rh, and Pd concentrations. Platinum and palladium uptake by magnetite was at a maximum at pH 6–7, and pH 3–4 for rhodium after 24 h with 0.1 mol/dm3 sodium chloride at an initial PGM concentration of 0.05 mol/m3. A sorption mechanism for PGMs was discussed based on the results.

Electrochemical investigation of gold uptake from chloride solution by magnetite

An electrochemical method (potential sweep method) was utilized to investigate the nature of the absorbed gold on magnetite and to determine the gold sorption mechanism. A magnetite electrode was prepared in the laboratory, made in contact with a gold chloride solution at different conditions, and was subjected to cyclic voltammetry. The cyclic voltammogram of the magnetite electrode pretreated in a gold chloride solution recorded an anodic current peak at around 1.0 V (vs. Ag/AgCl), which corresponds to the current generated for the anodic dissolution of metallic gold in a chloride medium. The results of the electrochemical experiments suggest that gold chloride complexes are reduced to metallic gold on the surface of magnetite. A four-stage gold uptake mechanism was proposed: (i) the transport of from the bulk solution to the magnetite surface, (ii) adsorption of ions on magnetite surface by electrostatic attraction, (iii) electrochemical reduction of to metallic Au, and (iv) the transport of soluble species to the solution phase. The electrochemical investigation also revealed that Fe3+ ions released from magnetite into the solution, suppressed the gold uptake at the acidic pH region.

Equilibrium modeling in adsorption of Re and Mo ions from single and binary aqueous solutions on Dowex 21K resin

Abstract The present study deals with the competitive adsorption of rhenium (Re) and molybdenum (Mo) ions onto Dowex 21K from single component and binary systems. The equilibrium adsorption data were obtained at different initial concentrations (50–250 mg/l), 12 h contact time, 290 K temperature, and resin dosage of 0.05 g at pH around 0.5. The single system equilibrium adsorption data were fitted via non-linear regression techniques to Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherm models. Both Freundlich and D–R isotherms for Re and Langmuir and D–R isotherms for Mo suitably described the adsorption equilibrium data. Equilibrium isotherms for the binary adsorption of Re and Mo ions onto Dowex 21K have been analyzed using Extended Langmuir, Modified Langmuir, Extended Freundlich and Langmuir–Freundlich models. The competitive Extended Freundlich model fitted the binary adsorption equilibrium data satisfactorily and adequately. Results of investigation on the mutual interference effects of Mo ions on Re adsorption capacity indicated that although Dowex 21K has generally higher affinity toward Re ions, the adsorption of perrhenate ions () is suppressed by a factor of about 49% in the presence of molybdenum ions. The adsorption of perrhenate ion is affected by competitive inhibition and shield preventing effects.

Regeneration of Sn4+ from Sn2+ solution during electrowinning process using anion exchange membrane

ABSTRACT Electrowinning process to regenerate Sn4+ from Sn2+ in HCl solution using an electrowinning cell with anion exchange membrane was proposed to suggest a novel recycling process to recover Sn. During the tests, the effects of initial Sn2+ concentration on the regeneration of Sn4+ were investigated under the following condition; 7,000 mg/L, 10,000 mg/L, and 13,000 mg/L of Sn2+, 1 M HCl, 250 A/m2 of current density, graphite anode, titanium cathode, room temperature, and 2 h. Electro-deposited Sn on the cathode showed dendritic structure regardless of the Sn2+ concentration and no change of Sn concentration was observed in the anolyte. Leaching tests were performed using the anolyte, obtained from the electrowinning tests, to examine the amount of regenerated Sn4+ concentration during electrowinning process. Based on the results of Sn leaching tests, it was found that 84.44%, 81.03%, and 79.43% of Sn4+ were regenerated from 7,000 mg/L, 10,000 mg/L, 13,000 mg/L initial concentration of Sn2+ solution, respectively. Consequently, it was found that the regeneration of Sn4+ can occur during the electrowinning process at the same time with Sn recovery and Sn4+ can be reused as an oxidant to leach Sn successfully.

Investigation on effects of ion exchangers structure and functional groups on the Re(VII) ions adsorption behavior from aqueous solution

ABSTRACT Alteration adsorption properties of Re(VII) on two resins with different functional groups and structure, weak base/macroporous and strong base/gel type, Purolite A170 (A170) and Dowex 21K (21K) respectively, were investigated experimentally and interpreted by isotherm, kinetic and thermodynamic modeling. Following the comparison of coefficient of determination values, the Freundlich and D-R isotherm models were found to be more suitable for description of investigated systems (R2 > 0.99). The Langmuir isotherm capacities (qm) were indicated that the perrhenate ions (ReO4−) adsorption is higher for weak base/macroporous type resin rather than the other at pH 3 in the presence of 50–250 mg L−1 Re (166.67 and 142.86 mg g−1, respectively). Also, the results from EDX studies corroborated this phenomenon. The adsorption reaction on both adsorbents was found to be chemically with mean free energy, E, as 12.18 and 13.62 kJ mol−1 for A170 and 21K, respectively. Kinetics of adsorption was studied by fitting the data into different mechanisms, among which the pseudo-second order mechanism was found successful for both used resins, but in case of 21K, the rate of perrhenate ions uptake was more rapid than A170. That is possibly attributed to the presence of strong base (quaternary amine) in functional groups. ΔG values obtained were all negative for both resins indicating a spontaneous adsorption process. The positive values of both ΔH (3.34 kJ mol−1) and ΔS (27.31 J mol−1 K−1) obtained suggest an endothermic reaction and in increase in randomness at the solid–liquid interface during the adsorption onto the A170 resin while for 21K, the negative changes in enthalpy and entropy provide an indication that the process is endothermic as well as it follows associative mechanism.

Mechanism and equilibrium modeling of Re and Mo adsorption on a gel type strong base anion resin

A static-batch technique was used to demonstrate the adsorption behavior of Re (VII) and Mo ions onto Dowex 21K at equilibrium in single and binary component systems. The single equilibrium adsorption data were modeled through a linear form of four widely used equilibrium isotherm equations. The results indicated that Freundlich and D-R models for Re, and Temkin and D–R isotherms for Mo fitted the obtained data satisfactorily. Binary adsorptions of Re and Mo ions onto Dowex 21K were also analyzed using Extended Langmuir, Modified Langmuir, Extended Freundlich and Langmuir–Freundlich models. The competitive Extended Freundlich model fitted the binary adsorption equilibrium data adequately. Studies on mutual interference effects of Mo ions on Re adsorption capacity indicated that the adsorption of perrhenate ions is always suppressed. In this perspective, the results from EDX studies confirmed the rhenium atom decrease in the simulated Re–Mo adsorption. However, under the studied conditions the affinity of the Dowex 21K for rhenium ions is marginally greater than that of molybdenum ions.