Comparison of neutralizing precipitation and zeolite adsorption for the removal of heavy metals in acid drainage

Abstract

Neutralizing precipitation and adsorption using zeolite as an adsorbent are examined and compared as methods for removing heavy metals from acid mine drainage and acid industrial wastewater. Both methods produced effluent satisfying standard pollutant levels from synthetic mine drainage (pH 2, Cd²⁺ 5 mg/L, Cu²⁺ 50 mg/L, Zn²⁺ 300 mg/L, Al³⁺ 300 mg/L, Fe²⁺ 1000 mg/L). However, neutralization produced almost twice as much sediment as zeolite adsorption. In the processing of synthetic acid industry wastewater (pH 2, Cr³⁺ 50 mg/L, Cd²⁺ 50 mg/L, Cu²⁺ 50 mg/L, Ni²⁺ 100 mg/L, Zn²⁺ 100 mg/L), all heavy metals in the precipitation-treated effluent except for Cd were below the standard level at pH 9-10, whereas all metals were reduced to below the standard with the addition of 40-60g/L of zeolite. The simple process of adding zeolite as an adsorbent simultaneously neutralizes and removes heavy metals from acid drainage. Zeolite, derived relatively cheaply from fly ash, therefore appears to be a highly suitable absorbent for the removal of heavy metals from acid drainage, and is expected to become highly cost-effective tool if a method for the regeneration of spent zeolite can be developed.