Enhanced Implications on Turbidity Removal from Natural Stone Wastewater by Binary Mixtures

The settling rate of the mineral fines in an aqueous solution changes depending on the charges they carry. Mineral fines with similar high-magnitude surface charges repel each other and prevent them from settling rapidly. In contrast, fines with no/low-magnitude surface charges can coalesce and agglomerate with the others and settle rapidly due to the increasing mass. This can lower the coagulant or flocculant use and speed up turbidity removal. Thus, considering this fact, the experimental tests in this study were performed below the neutral pH environment (pH 2–6) to determine the effectiveness of the coagulant and flocculant mixtures and compare the results with their single use. The turbidity removal tests were applied using different valence coagulants and flocculants with different charge mechanisms. According to the results with their single use, the best results were obtained using FeCl3 (80 mg/L) at pH 4 with a turbidity removal efficiency of ≤98% and a nonionic flocculant at pH 2 with a turbidity removal efficiency ≥99% (0.50 mg/L). When they were used as binary mixtures, the lowest turbidity values were obtained with FeSO4/nonionic flocculant mixtures at pH 4 (≤98%) and with FeCl3/anionic flocculant mixtures at pH 2 (≥99%).