KINETICS OF ION REMOVAL FROM AN IRON-RICH INDUSTRIAL COPRODUCT .3. MANGANESE AND CHROMIUM

An iron-rich material (IRM) contained the potential soil and water pol lutants Mn and Cr. Therefore, to assess the feasibility of using the I RM in agricultural and nonagricultural settings, this study was conduc ted to determine the processes and kinetics of Mn and Cr (total solubl e metals) retention and removal from the IRM. This was accomplished by employing adsorption isotherms, column studies, and the stirred-how ( SF) kinetic technique. Manganese adsorption conformed to the Langmuir equation and Cr adsorption was described by the Freundlich equation. T he kinetic studies showed that indigenous Mn salts were depleted insta ntaneously via a volume-dependent process. Both Mn and Cr in the IRM b ecame solubilized while being processed at the industrial plant. But, unlike Mn, Cr was readsorbed by the IRM after the initial solubilizati on. This fraction of the Cr was desorbed rapidly, conforming to first- order kinetics and yielding a rate-constant of 0.56 min(-1). After the rapid removal of some of the Mn and Cr, a steady-state with wodginite may have governed Mn removal, and chromite may have controlled the Cr concentration, through zero-order dissolution reactions. Both column and SF studies showed that the proportion of total soluble (dischargea ble) Mn and Cr was small.