Removal of cationic and anionic pollutants from water solutions using Ukrainian limestones: a comparative analysis

Removal of cationic and anionic contaminants from surface waters with the same natural material is relevant both from environmental and economic points of view. Cationic contaminants can be removed by adsorption, while anionic ones - by the formation of insoluble calcium salts. In this study, nickel was taken as an example of a cationic pollutant and phosphate - an anionic pollutant. To test the removal efficiency of these substances, natural limestone and dispersed, thermally activated limestone were compared. Dispersed, thermally activated limestone gave better results of Ni2+ and PO 43- removal from all water solutions than natural limestone. This was due to its dispersion and subsequent heating to 240 degrees C-250 degrees C. As a result, limestone was destroyed and the calcite crystals broke apart. The doses of limestone were 2.0 and 4.0 g/L, the initial pH was 5 and 7, and the total dissolved solids (TDS) was at 0.02 and 0.55 g/L. Measurements of changes in the pH, Eh and TDS values were carried out. At water pH increase, the efficiency of Ni2+ removal decreased, while the efficiency of PO 43- removal increased. For purification of surface water by limestone, the selection of its type and dose depends on the usage of the water body.