BIO11) Batteries recycling process using local isolated thermopile culture

Introduction Batteries are used daily in many portable electronic devices. Therefore spent batteries represent, within the wastes, an important environmental pollutant in terms of heavy metals content. Considering the risk associated with uncontrolled disposal of these batteries a legislation on disposal and recycling of spent batteries must be formulated. The development of a metal recovery processes is thus convenient from an economic and environmental point of view (i.e. high cost of landfill disposal of hazardous material, waste recycling and natural resources conservation). Metallurgy is the science and art of extracting and refining metals. The two basic processes for recovering metals are called hydrometallurgy and pyrometallurgy. In pyrometallurgy, the chemical action is carried out by means of heat supplied by the burning of fuel, the operation usually taking place in a furnace. The pyrometallurgical method in batteries leaching consists basically of selective volatilisation of metals at elevated temperatures followed by condensation. For example, cadmium is recovered from Ni–Cd batteries by volatilisation at temperatures around 900 C and zinc and mercury from zinc–carbon and alkaline batteries at 1500 C. The current commercial technology is pyrometallurgy based i.e. BATREX, RECYTEC, SNAM-SAVAN, SAB-NIFE and INMETCO (de Souza et al., 2001). However, these technologies are energy consuming and produce some emissions of dust and gases (Salgado et al., 2003). Hydrometallurgical processes involve leaching the metal content from its sources in an aqueous solution, from which the metal may then be recovered. Recently, some hydrometallurgical processes have been developed to recover metals from these secondary sources. The benefits coming from a hydrometallurgical process are: complete recovery of metals at high purity, low-energy requirements, avoidance of air emissions and minimization of wastewater. In the case of hydrometallurgical treatments of waste, the metal content in a solid material is mostly dissolved in liquid medium (acid, ferric or ammonia solution) and processed to recover metal ions. However, large amounts of chemicals are consumed, making the process uneconomical. Bioleaching (biohydrometallurgy) refers to the use of bacteria to extract or leach metals. This technology has become increasingly important due to its simplicity, low cost and applicability to low-value metals. Bioleaching application was dominated by the mining industries. Recently, applications of bioleaching in waste detoxification have attracted a lot of scientific interest. However, the development of bioleaching applications in the industries is predicted to be limited due to the slow leaching rate (Bosecker, 1997). Sequential chemical-biological leaching approaches have been exploited in the mobilization of metals in batteries using bacteria. Application of bioleaching technology with the chemical pre-leaching step has been explored to treat a multi type of dry batteries. This technique offers the most economical, safe and efficient process for decontamination of solid waste The bioleaching of dry cell batteries is the first project of its kind in Malaysia. The absence of this technology will lead to huge amounts of our resources of metal being left idle which can then pose a treat to the environment