Kinetics of Ion Removal from an Iron‐Rich Industrial Coproduct: III. Manganese and Chromium

Abstract

AbstractAn iron‐rich material (IRM) contained the potential soil and water pollutants Mn and Cr. Therefore, to assess the feasibility of using the IRM in agricultural and nonagricultural settings, this study was conducted to determine the processes and kinetics of Mn and Cr (total soluble metals) retention and removal from the IRM. This was accomplished by employing adsorption isotherms, column studies, and the stirred‐flow (SF) kinetic technique. Manganese adsorption conformed to the Langmuir equation and Cr adsorption was described by the Freundlich equation. The kinetic studies showed that indigenous Mn salts were depleted instantaneously via a volume‐dependent process. Both Mn and Cr in the IRM became solubilized while being processed at the industrial plant. But, unlike Mn, Cr was readsorbed by the IRM after the initial solubilization. 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 (dischargeable) Mn and Cr was small.