the effectiveness of land treatment for removal of heavy metals

land treatment method of municipal and industrial wastewaters for utilization of nutrients in the wastes for raising useful crops and tertiary(or advanced) treatment of the water for improving stream quality or to recharge falling water tables is increasing in some parts of the world, particulary in the arid area. as emphasis in this type of treatment method and prevention of surface and underground waters from contamination, it becomes necessary to estimate efficiency of land treatment in removing other types of contaminan~ ts including heavy metals. in this paper, the results of adsorption and desorption tests of mercury, arsenic, and cadmium by various soil and se4iment constituents, instabilit¥ coefficients, and isothermal adsorption and desorption data have utilized for evaluation of the land tratment efficiency in removing heavy metals. inorganic mercury had a high affinity for sulfur containing soils, clays and synthetic scavengers such as silicon alloys, anionicion exchange resins and activated carbon. the desorption of inorganic mercury was found to be of the following order: 10% for sandi> 1% for clay organi cs (not observed). methylmercury had a high affinity for sulfhydryl containing minerals and three dimensional clays such as montmorillonite and illite. desorption of methylmercury was simila~ to inorganic mercury. inorganic cadmium was found to have a high affinity for oxide minerals,sulfhydryl containing organics and threedimensional clays such as illite and clinoptilotite. generally, the oxides exhibited a very low desorption rate except at severe levels of calcium, chloride and ph