ASSESSMENT OF INTERFERENCE IN BIOSORPTION OF A HEAVY-METAL

Nonliving biomass of Sargassum, a brown marine alga, is capable of bin ding more than 10% of its dry weight in toxic cadmium ions. Although u biquitous iron interferes with Cd uptake, only approximately 4.5% of i t is sequestered (biomass dry weight). Biosorption of both metals at p H 4.5 could be described by Langmuir-type isotherms with b, the affini ty-related coefficient (Cd: b = 0.015; Fe: b = 0.027). The interferenc e of Fe with Cd uptake, and vice versa, was assessed by deriving three -dimensional equilibrium two-metal sorption isotherm surfaces, smoothe d and ''cut'' to reveal the inhibition effect of Fe on biosorption of Cd: at the equilibrium concentration Cf [Cd] = 1.5 mM, the presence of Fe at 1.5 mM equilibrium concentration suppressed the Cd uptake to on ly 76% of the original value. For 50% Cd uptake reduction, a very high equilibrium Fe presence of 4.5 mM was required. The Cd presence affec ted the uptake of Fe very strongly. To obtain equal values of uptake f or each metal in the biosorbent, the ratio of equilibrium concentratio ns of 0.42 Cd to 1 Fe is necessary in the liquid phase. (C) 1997 John Wiley & Sons, Inc.