Phosphorus sorption by natural calcite and the effects of pH and grain size
不同粒径方解石在不同pH值时对磷的等温吸附特征与吸附效果

Phosphorus sorption characteristics of natural calcite at different pH values and different grain sizes were studied in the laboratory. A series of phosphate concentration was set in laboratory, then 1 gram calcite with 4 group of different grain size was added at 3 different pH values that is 9.00±0.02, 7.00±0.02, and 6.00±0.02 respectively in 50 milliliter centrifugal cubages. Calcite samples of different mesh sizes were tested for their sorption of phosphorus at pH=9, 7 and 6. Analysis of the experimental data showed that the sorption isotherms fit the Freundlich equation at all 3 pH values, but fit the Langmuir equation only at pH=7. The smaller the calcite grain size, the better the phosphorus sorption effect of natural calcite became. Calcite with 325 mesh had the best sorption effect of phosphorus under the experimental conditions. The pH is an important factor influencing phosphorus sorption by calcite. At pH=6, the sorption effect of phosphorus is better due to an increase of the concentration of Ca2+ from dissolution and favorable conditions for combination with PO3-4 to form a Ca-P compound. At pH values greater than 7, phosphorus is considered to be removed by calcite adsorption, codeposition of phosphorus and calcite, and formation of crystalline Ca-P compounds. Overall, the phosphorus removal rate at pH 9 is better than at pH 7.