(539d) Effect of Organic Anion On Selective Adsorption

Authors: 
Koong, L. F., The Hong Kong University of Science and Technology
Lam, K. F., The Hong Kong University of Science and Technology
McKay, G., Hong Kong University of Science and Technology
Barford, J., Hong Kong University of Science and Technology



Metal containing waste such as electronic waste is the fastest growing waste in the world and they pose a great challenge to waste management and disposal. Today we are not only interested in metal removal, but also recovery especially from waste, due to the dwindling metal reserves.  Many researches have looked into leaching metals from batteries, printed circuit boards, magnet etc. Adsorption could make a good application in metal recovery from leachate due to its simple application and ability to operate at low concentration levels. Selective adsorption will be especially useful in recovering individual metal, especially in wastewater or leaching medium where multiple metal species can be present. The selectivity is strongly dependent on the interactions between the functional groups on the adsorbent and the metals. Another factor that could affect selectivity is the metal speciation. Organic anions are able to form complexes with metals, which can then affect the adsorption capacity, and most importantly, selectivity. Organic anions can be naturally found in water environment, the organic acids and derivatives also find wide applications in industry, such as textile, drug, paper, electroplating and so on, and therefore it is important to investigate the influence of anion on adsorption mechanism. This paper aims to demonstrate the effect of organic anions on selectivity of metals using the example of Copper and Cadmium in different anion system: nitrate, sulfate, acetate and formate salt. Iminodiacetic acid resin and chitosan are used in this study. It was found that when organic anions of COOH-based are present, the adsorption capacity is affected but not the selectivity, which Cu is still preferentially adsorbed. However, when amine based organic anions are present, the selectivity can be affected due to stronger complexation between the metal and anions. To demonstrate this EDTA is added to into the nitrate system of Cu-Cd and it is observed that Cd can be selectivity adsorbed at a right concentration of EDTA. EDTA is also removed by adsorption to return the selectivity back to Cu. Total Organic Carbon Analyzer is used to measure the concentration of EDTA in this case.