Abstract: Klean Earth Environmental Company (KEECO) has developed the Silica Micro Encapsulation (SME) technology to treat heavy metals and radionuclides in water and soil. Unlike conventional neutralization/precipitation methods, SME encapsulates the contaminants in a permanent silica matrix resistant to degradation under even extreme environmental conditions. Encapsulated metals and radionuclides are effectively immobilized, minimising the potential for environmental contamination and impacts on human or ecosystem health. The effectiveness of SME has been proven through independent reviews, laboratory and field trials and commercial contracts, and the technology can be used to control and prevent acid drainage and the transport of soluble metals from mine sites, tailings areas, landfills and industrial sites. Successful demonstrations in the treatment of sediments and in brownfield redevelopment, treatment of metal-finishing wastewaters, and control of hazardous, low-level, and mixed waste at DOE/DOD sites and commercial nuclear power plants have also been undertaken. This paper describes the reactions involved in the SME process, the methods by which SME chemicals are introduced to various media, and recent project applications relevant to the cost effective remediation and prevention of environmental problems arising from energy and mineral production.