New method for evaluation of heavy metal binding to alginate beads using pH and conductivity data

Extensive research has been conducted for removal and recovery of heavy metals from wastewater and industrial wastewater in recent years. Due to its low cost and high sorption efficiency, alginate was extensively investigated as a biosorbent. It is known that the sorption of metals to alginate is rate limited. However, the sampling in the beginning of experiments, from 30 seconds to few minutes, is very difficult, if not impossible. In this study, a nontraditional experimental method was used to determine the removal kinetics of metals for short time periods. A relationship among pH, conductivity, and metal concentration was established. It was shown that the sorption mechanism was ion exchange for all metals investigated in this study. A series of experiments was conducted to determine the ion exchange kinetics of different metals at varying pH conditions. Second order pseudo rate kinetics was shown to define the experimental findings well. Results also showed that the extent of exchange significantly reduced as the pH decreased. The selectivity of metal exchange to alginate beads was determined. It was observed that the extent of the ion exchange was greatest for Cu^{2 +} and lowest for Mn^{2 +} and Fe^{2 +}, following the order of Cu^{2 +} > Zn²⁺≅ Co^{2 +}≅ Ni²⁺ > Mn²⁺≅ Fe²⁺.