Fine particle removal from natural stone processing effluent by flocculation

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In this study, the sedimentation behaviors of five different natural stones (i.e., marble and travertine suspansions) were examined by applying classical sedimentation tests. The suspensions were first characterized using electrokinetic and physical analysis techniques and then subjected to gravity and flocculation aid sedimentation tests to find the effect of process parameters on the treatment process, such as contact time, sample composition, and the concentration of polymers. The electrokinetic measurement results of the samples clearly indicate that the source of the suspensions profoundly affect the sing of the surface potential. The marble samples mainly exhibit positive surface charges while the travertine samples have negative values in the studied pH range. The flocculation aid sedimentation tests performed at the polymer dosages of 0.16, 0.80, and 1.6 mg/L reveal that the settling times needed for complete sedimentation decreased from 12 h to approximately 20 min with the use of flocculant compared to gravity sedimentation. It was also observed that the use of an anionic flocculation reagent is more effective on the sedimentation rate of the suspended particles and the turbidity of the supernatant solutions compared to cationic or non-ionic reactive uses. Consequently, the turbidity of the waste solutions could be decreased from <20,000 NTU to 20 NTU by flocculation aid sedimentation within 15 min of the settling time. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 317-324, 2013