Evaluation of zeta potential and particle size measurements of multiple coagulants in semiconductor wastewater

Abstract

Chemical precipitation method utilizing calcium salts has been extensively used to treat fluoride-containing wastewater from semiconductors industries. Aim of this paper it to investigate the coagulation behavior of calcium salts (CaCl2), aluminium salts (PACl) and polymer by using dynamic light scattering technique that is applied as an alternative methodology to pre-determine the optimum pH and dosage range. The stability and behavior of the wastewater sample and coagulants were studied in terms of zeta potential and z-average hydrodynamic diameter profiles as a function of pH (pH 2 to 12). It is observed that optimum pH range and dosage range for fluoride-containing wastewater, CaCl2, and PACl were at pH 9, pH 5 with 3 mg/L CaCl2, and pH 7 with 1 mg/L PACl, respectively. This condition is followed by the addition of polymer which act as a flocculant at three different pH regimes; pH below than pHPZC (pH pHPZC). Experimental results indicated that addition of polymer at pH=pHPZC (CaF2/PACl at pH 5) and dosage of 2 mg/L promotes the biggest size of z-average hydrodynamic diameter of the particles which is 4500±0.9 d.nm with zeta potential value of 0.2±0.1 mV. Therefore from this study proved that pH adjustment played an important roles during coagulation and flocculation process especially in aggregation or disaggregation of the particles.