Effects of surface properties of organic matters on cation adsorption in solution phase

Organic substances have been commonly added to mine tailings to improve physical and chemical conditions and facilitate plant establishment. Apart from their nutritional benefits, aggregation and physical improvements may be resulted from organo-mineral interactions between their functional groups and cations of variable charges on mineral surfaces. Organic matters (OM), e.g., woodchips (WC) and sugarcane residue (SR), were initially evaluated for their affinities for Cu, Ca, and Fe in relation to their surface properties at constant or different pH conditions in aqueous phase, before examining the formation of organo-mineral association in solid phase. Results indicated that WC and SR had different adsorption kinetics for these cations. Their surface negative charges indicated by zeta potentials were positively related to the adsorption capacities. 13C NMR analysis of the OM before and after adsorption revealed that carboxylic and phenolic groups were the major contributors to cation adsorption in solution. SR was found to have more carboxylic groups and thus had higher cation exchange capacity than WC. Therefore, organic materials with high density of functional anion groups on the surfaces may be advantageous when stimulating organo-mineral interactions in mine tailings which are rich in primary and secondary minerals with positively charged surfaces. The organomineral association between the OM and base metal mine tailings will be examined in the solid phase in a follow-up experiment