Environmental Pollution Remediation through Solidification/Fixation of Heavy Metal Ions in Portland Cement

Abstract

Environmental Pollution Modern civilization equipped with advanced science and technological skill is rapidly transforming the earth to a modern world through developmental activities thereby creating numerous ecological problems and environmental pollutions associated with the hazards to human beings. These development activities have enhanced the productivity at the cost of exploitation of natural resources. The addition and accumulation of such unwanted materials or things into the environment causes destruction and degradation in ecology. The knowledge of environmental chemistry serves as a key to the understanding of water, land, air and soil pollution that may be caused through biological, chemical and physical activities [1,2]. As the amount of hazardous industrial wastes accumulates due to rapid industrialization, its planned management is required to reduce adverse impact on human beings and ecosystem. The type of waste, cost, legislation and technology limits the disposal options for industrial waste. Organic wastes with high calorific values are generally treated by oxidation or incineration, whereas inorganic wastes, commonly found in aqueous solutions or suspensions often require pretreatment before landfill. Among the industries with highest emission of heavy metals are the mining industry, metallurgical industry, chemical industry, leather industry, sugar industry, paper industries, distilleries, battery industry and thermal power plants. Toxic metals are added in the aquatic system from industrial processes, domestic sewage discharge, street dust and fossil fuel burning. All these waste streams containing heavy metal ions with very low organic content require treatment before disposal. The continuously increasing demand for raw materials and the limited availability of natural resources gave rise to the investigations of the by-products of the industry for possible reuse. Studies have shown that solidification/chemical fixation of toxic heavy metals and hazardous wastes using cement, lime, pozzolanas and other inorganic materials have been attempted to a limited extent in some of the developed countries [3]. These processes involve mixing the waste with a binder material to enhance the physical properties of the waste and to immobilize contaminants that may be detrimental to the environment. This method, effective at times, has been designated the best demonstrated available technology for some wastes and wastes forms and the United State Environmental Protection Agency has approved its use for clean me up of certain sites [3-5]. The toxic waste generated from industries containing heavy metal ions namely cadmium, nickel, mercury, zinc, copper, lead, arsenic, chromium, etc. reach the ground and contaminates soil and water [6] (Figures 1 and 2). Some of the heavy metals are essential for life processes where as others like Cd, Pb, and Hg have no known useful biological role. All of them are injurious to living organisms at higher concentration. The heavy metals have great affinity to sulphur and attack sulphur bonds in enzymes, thus immobilizing the later. Heavy metals bind to cell membrane, affecting transport process through the cell wall. They also tend to precipitate phosphate bicompounds or catalyze their decomposition. Soil and water are characterized by varying degree of metal contamination. Air, soil and water contribute a significant Abstract Treatment of hazardous wastes existing as effluent using cement-based solidification/stabilization is an effective option for remediating environmental pollution. Among the various treatment techniques, it is one of the most widely acknowledged methods for treating the wastes. The primary objective of this review is to survey our current knowledge in this subject, focusing on cement chemistry, the effects of inorganic (heavy metals) and organic compounds on cement hydration and the mechanisms of immobilization of different organic and inorganic compounds. clay grinding Figure 1: The cement cycle.