Removal and recycling of copper from aqueous solutions using treated Indian barks

Removal of copper from aqueous solutions containing 100-1000 ppm, using different Indian bark species, was performed on laboratory scale. The percentage removal of metal ions depends on the solution pH, bark species and time. The efficiency of copper removal by the used raw barks increases with a rise of solution pH and reaches a maximum of about 65-78% around pH 4-5. However, the decontaminated aqueous solutions were colored due to the dissolution of soluble organic compounds contained in the raw bark. This increases the biological and chemical oxygen demand (BOD and GOD) of the solutions as well as the total organic carbon content (TOC). For this reason, raw bark should be treated either by chemical or biological means. Such treatment will allow the extraction of the soluble organic compounds and increase the chelating capacity and efficiency of the treated bark. Depending on the pH value, the chelating efficiency of treated barks is about 1.2-2.2 times that of the raw ones. Moreover, the retention capacity of the Indian treated bark varies from about 42-51 mg/g of dry bark. It is equal to or higher than that of common European species. About 1.8 mols of H3O+ are released, by the treated barks, for every mol of chelated copper ions. Moreover, scanning electron microscopy (SEM) observations show uniform distribution of metal ions throughout the copper saturated bark. Infra red (IR) spectra suggest that the copper ions are chelated to hydroxyl and/or carboxyl functional groups of organic compounds contained in the treated bark. It seems that the interaction of the copper ions with the bark follows a cation exchange mechanism. This hypothesis is supported by elution experiments that allow recovery of about 99% of the contained copper. The retention capacity of the treated bark is almost constant after five cycles of chelation-elution, suggesting that the 'life time cycle' is sufficiently long for continuous industrial application. The spent copper loaded barks can either be incinerated or pyrolysed. It generates solids containing either approximate to 80% of CuO or approximate to 14% of Cu-o, respectively. Such materials can be used either in the secondary or primary copper production, thus offering a friendly environmental solution of effluents' treatment. The suggested process can be used as an alternative to the classical technologies for effluent decontamination. It is also efficient for polishing effluents treated by other methods. (C) 1997 Elsevier Science B.V.