Elimination of inorganic mercury from waste waters using crandallite‐type compounds

Abstract

AbstractThe removal of inorganic mercury from waste water streams arising from mines, using an artificial amorphous compound of the crandallite type synthesized in our laboratory, Ca0.5Sr0.5Al3(OH)6(HPO4) (PO4), has been investigated. This compound exhibits an extremely wide range of ionic substitutions: Ca2+ and Sr2+ were interchanged with Hg2+, so the mercury content of the waste water, ranging from 70 to 90 ppm, was reduced to less than 0.1 ppm. The process has been studied under batch conditions. The crandallite showed a high capacity for the exchange of mercury from mercuric nitrate solutions, 1.555 meq g−1. The ion‐exchange equilibrium isotherms for Hg2+ were correlated by the Langmuir equation. The recovery of mercury from Hg‐crandallite using HCl solutions and thermal treatment was also studied. Optimum recuperation of mercury is achieved by chemical reaction with HCl solution (pH 2.25). At these conditions, 75% of the mercury is recovered as the HgCl42− complex in a simple batch process, and the crandallite (in the protonic form) can be reused.© 2003 Society of Chemical Industry