Agricultural biomasses as sorbents of some trace metals

The studies of sorption of six metal ions (Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Cr³⁺ and Cr(VI)) from by-products of agriculture are taken into account. The Langmuir q_max values obtained with the use of different biomasses are evaluated and, in order to acquire comparable results, the necessity of using molar concentrations is stressed. The main effects of pH on sorption are estimated by considering both the behaviour of metal ions (hydrolysis and hydroxide precipitation) and the effect of pH on coordination, using a simulated example. Some considerations are made on the information that can be obtained using the most common isotherms and on the need to use chemical dimensions rather than weight in order to make comparison among various metal ions (since atomic weight differences deeply alter the significance of parameters in non-chemical units) and to predict the effects of competition between two (or more) of these for the same sorbent sites on the biomass surface.