Effects of Alum Sludge Characteristics on the Efficiency of Coagulants Recovery by Acidification

Due to Technological advancement cathode-ray tubes (CRTs) from computer monitors and TV sets are being replaced continuously by thinner and lightweight versions like Liquid Crystal Display (LCD) or Plasma screen monitors. As regular discarding e-waste from CRTs are continuously increasing day by day and in UK alone it is projected to reach around 100,000 tonnes/year. CRT composition consists of 50-72% SiO2, 10-15% PbO, 5-7% Al2O3 and 18-35% various oxides with 00.5% of bonded plastics and carbon. From the recycling point of view this waste is categorized into two parts; (i) Organic decomposable part and; (ii) Silicate with metal oxide part. Management of CRTs involves the following steps; (i) grinding and milling; (ii) Thermal decomposition of organic part and finally; (iii) silicates with metals oxides are then subjected to thermal and/or ionic treatment in the presence of fluoride to produce molecular sieves for various applications including separation chemistry. Thermo/ ionic reactions were performed at temperature between 500-6250C and in the presence of fluoride ion in such a way that 98% of the fluoride used can be recovered finally. Silica and metal oxide (mostly heavy metals) mixture from waste CST: (i) pose serious environmental problem when landfilled due to heavy metal leaching and; (ii) the separation of heavy metals from silica is an expensive operation. It justifies the significance of Thermo/ ionic reactions for the purpose. It was found that the product from thermionic reaction have more crystalline pattern as compared with thermo reaction, as confirmed by XRD and SEM analysis.