Modeling chemical speciation of copper in River Yamuna at Delhi, India

Chemical modeling of copper in the river Yamuna was attempted by an equilibrium constant method, using a computer program COCSOC developed for the purpose. Concentrations of metals (Cu, Ca and Mg), ligands (organics, carbonates and bicarbonates) and stability constants of the probable complexes were the inputs for the modified Newton-Raphson iteration. The model adequately predicted concentrations of various copper species, even without taking into consideration solid phases, other competing metals and ligands. The free cupric ion concentrations estimated were in the range of 10(-17) to 10(-16) M, undetectable by ion selective electrodes in the water from the river. The non-convergence of equilibrium computations for certain data sets at some sampling sites indicates the prevailing non-equilibrium conditions in the river due to large-scale release of ligands and metal ions through several drains.