Abstract
In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant familiesof materials, existing both as several minerals and being produced synthetically. Notable examples include quartz, crystal, fumedsilica, silica gel, and aero gels. Applications range from structural materials to microelectronics to components used in the foodindustry.Silica exposure remains a serious threat to nearly 2 million U.S. workers, including more than 100,000 workers in high risk jobssuch as abrasive blasting, foundry work, stonecutting, rock drilling, quarry work and tunneling. Crystalline silica has been classifiedas a human lung carcinogen. Additionally, breathing crystalline silica dust can cause silicosis, which in severe cases can be disabling,or even fatal. The respirable silica dust enters the lungs and causes the formation of scar tissues, thus reducing the lungs’ ability totake in oxygen. There is no cure for silicosis. Since silicosis affects lung function, it makes one more susceptible to lung infectionslike tuberculosis. In addition, smoking causes lung damage and adds to the damage caused by breathing silica dust. in water supply,silica can exist in a dissolved, particulate or colloidal form. A colloid is a very fine suspended particle which does not settle readily. Inhigh enough concentrations, silica has a tendency to form scale deposits. This is especially true in high temperature boiler applicationsand in the power generation field where silica can deposit on turbine heads. Treatment for silica depends on the form it’s in. In theparticulate form, silica can be removed by simple filtration. The colloidal form may require chemical addition such as magnesium saltsfollowed by filtration or reverse osmosis (RO). In the dissolved form, RO and anion exchange work well, however anion exchange isnot generally practiced in domestic applications as it requires caustic soda to strip the silica back off. Needless to say, silica removal isnot as easy as it appears.As contribution to solve the mentioned problems in industrial wastewater, coagulation and flocculation experiments were carriedout to assess the ability of coagulant made mainly from paper sludge ashes (PSA) for the removal of high concentration colloidalsilica wastes from microelectronics industry. Three different parameters were checked, pH, coagulant dosage, and temperature. Highremoval efficiency was obtained when pH was higher than 8, therefore no need to adjust pH before treatment since waste is producedwith high pH values. The optimum coagulant dosage was 0.25 g of PSA per 1gram of silica at concentration of 1.8% colloidal silica.Temperature was carried out under mild conditions from (10-40 oC). Increasing the coagulant dose at 10 oC or lower could help toachieve clear effluent. Long-term operating data were gathered by using continuous flow system for treatment actual wastes. Averageresults obtained for the fluent for TN, TP, T. Si, COD, BOD and S.S were 11, < 1, < 50, 10, 12 < 50PPM, 16 PPM, and <100 PPMrespectively which are comply with the most international environmental regulations.