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This paper studied the removal of heavy metals from gold mining effluent (GME) of the AngloGold Ashanti mine (Obuasi, Ghana) in continuous down-flow fixed bed columns using coconut shell and iron oxide-coated sand as sorbents operated at a temperature of 28±2°C and a constant flow-rate of 150mLmin−1. The two-stage treatment system targeted the removal of copper and arsenic, but other heavy metals (iron, lead and zinc) present in the GME in very low concentrations were also removed, with removal efficiencies exceeding 98% for all metals in all the cases studied. A total of 14.8m3 of GME was treated in 1608h before arsenic breakthrough occurred in the system. At that point, copper, iron, lead and zinc were still completely removed, leaving no traces of the metals in the treated effluent. Copper uptake amounted to 16.11mgg−1, which is 2.23 times higher than the value obtained in a single ion laboratory column study. Arsenic and iron uptake amounted to 12.68 and 5.46mgg−1, respectively. The study showed that the two-stage treatment configuration is an ideal system for the simultaneous removal of copper and arsenic from low concentration GME, in addition to other heavy metals present at low concentrations. [ABSTRACT FROM AUTHOR]

Sorption is a viable treatment technology for copper-rich gold mine tailings wastewater. For continuous application, the sorbent should be regenerated with an appropriate desorbent, and reused. In this study, the sequential sorption/desorption characteristics of Cu(II) on coconut shell (CS) and iron oxide coated sand (IOCS) were determined. In batch assays, CS was found to have a Cu(II) uptake capacity of 0.46 mg g−1and yielded a 93% removal efficiency, while the IOCS had a Cu(II) uptake capacity and removal efficiency of 0.49 mg g−1and 98%, respectively. Desorption experiments indicated that HCl (0.05 M) was an efficient desorbent for the recovery of Cu(II) from CS, with an average desorption efficiency of 96% (sustained for eight sorption and desorption cycles). HCl (0.05 M) did not diminish the CS's ability to sorb copper even after eight sorption/desorption cycles, but completely deteriorated the iron oxide structure of the IOCS within six cycles. This study showed that CS and IOCS are both good sorbents for Cu(II); but cyclical sorption/desorption using 0.05 M HCl is only feasible with CS. [ABSTRACT FROM PUBLISHER]

Adsorption kinetic studies are of great significance in evaluating the performance of a given adsorbent and gaining insight into the underlying mechanism. This work investigated the sorption kinetics of Cu(II) on to coconut shell and Moringa oleifera seeds using batch techniques. To understand the mechanisms of the biosorption process and the potential rate-controlling steps, kinetic models were used to fit the experimental data. The results indicate that kinetic data were best described by the pseudo-second-order model with correlation coefficients (R 2) of 0.9974 and 0.9958 for the coconut shell and Moringa oleifera seeds, respectively. The initial sorption rates obtained for coconut shell and Moringa oleifera seeds were 9.6395×10−3 and 8.3292×10−2 mg g−1 min−1, respectively. The values of the mass transfer coefficients obtained for coconut shell (1.2106×10−3 cm s−1) and Moringa oleifera seeds (8.965×10−4 cm s−1) indicate that the transport of Cu(II) from the bulk liquid to the solid phase was quite fast for both materials investigated. The results indicate that intraparticle diffusion controls the rate of sorption in this study; however, film diffusion cannot be neglected, especially at the initial stage of sorption. [ABSTRACT FROM PUBLISHER]