Purification of natural stone wastewaters with flocculation/coagulation method

In this study, flocculation and coagulation mechanisms in purification of natural stone(i.e., marble and travertine) wastewaters in suspension form resulting from processingof natural stones have been tried to explain. In the experiments, polyacrylamide basedanionic, cationic and nonionic flocculants and different type coagulants were usedand two different types of natural stone suspensions (NSS), marble suspension andtravertine suspension, were used as representative samples for original natural stonewastewaters. Purification performances of NSS were assessed under the data ofsettling rate of flocculated suspension and that of turbidity of c1ean water obtainedafter each settling test.In the first step, zeta potential measurements of marble and travertine powders inwater versus pH and their mineralogical, chemical and partic1e size analysis weredone. In the second step, sedimentation tests using flocculation, coagulation and"coagulation + flocculation" methods have been applied on the NSS. In the scope ofsedimentation tests, firstly the effects of flocculant type, molecular weight, chargedensity (anionicity degree), and dosage and suspension pH on flocculation of naturalstone suspensions (NSS) were investigated. Consequently, optimum conditions anddominant mechanism for their flocculation were determined. Then, coagulant type,dosage and pH parameters were studied on travertine suspension, and accordingly,coagulation mechanism(s) of NSS were determined. In addition, "coagulation andflocculation" method has been applied on travertine suspension. As a result, the bestmethod or methods and condition(s) to clarify natural stone wastewaters usingaggregation techniques such as flocculation and coagulation were determined.Key words: Marble, Travertine, Wastewater, Flocculation, Coagulation, SettlingRate, Turbidity, Polymer (Flocculant)