Abstract: This paper describes the genesis, structure and classification of natural zeolites, including their most relevant properties such as porosity, adsorption and ionic exchange. The use of natural zeolites in the treatment of effluents containing heavy metals is reviewed based on current literature. These uses are focused on mineral-metallurgical effluents and mercury pollution related to artisan mining activities. The study shows that natural zeolites are efficient in removal of heavy metals in metal mining effluents, can be produced and improved at a low cost, and can also be used to adsorb mercury vapors from ovens used to fire amalgams.

Abstract: When designing wetland treatment systems for trace metal removal, both aerobic and anaerobic processes can be incorporated into the final design. Aerobic processes such as adsorption and ion exchange can successfully treat neutral drainage in overlandflow systems. Acid drainage can be treated in anaerobic systems as a result of sulfate reduction processes which neutralize pH and precipitate metals.Test work on both aerobic and anaerobic systems has been conducted in Minnesota. For the past three years, overland flow test systems have successfully removed copper, cobalt, nickel and zinc from neutral mine drainage. Nickel, which is the major contaminant, has been reduced around 90 percent from 2 mg/L to 0.2 mg/L. A sulfate reduction system has successfully treated acid mine drainage for two years, increasing pH from 5 to over 7 and reducing concentrations of all metals by over 90 percent.Important factors to consider when designing wetlands to remove trace metals include not only the type of wetlandrequired but also the size of the system and the residence time needed to achieve the water quality standards.