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

以天然方解石为材料,研究了不同pH值与不同粒径方解石对磷吸附效果的影响.实验设置了不同质量浓度磷系列溶液,加人1g不同粒径,即小于100目、100～180目、180～325目和325目的方解石,在PH值分别为9.00±0.02、7.00±0.02和6.00±0.02时.研究方解石对磷的吸附效果,并用Langmuir模型和Freundlich模型对等温吸附线进行了拟合.结果表明,方解石对磷的吸附等温线能较好地用Freundlich方程来拟合.方解石的粒径越小,对磷的吸附能力越强,在本实验选取的粒径范围内,325目方解石对磷酸盐的吸附效果最好;但180～325目方解石对磷的吸附能力与325目方解石的差别不大,实际应用中,选用180～325目方解石即可取得对磷的较好的吸附效果.pH值是影响方解石吸附磷的重要因素,pH为6时,由于方解石微溶产生的Ca2 与水体中PO3-4结合形成Ca-P化合物,使其吸附磷效果较好;pH≥7时,通过方解石吸附作用、与碳酸钙共沉作用及以方解石作为结晶核的钙磷化合物结晶作用去除磷;pH为9时方解石对PO3-4吸附效果好于pH值为7时.

Phosphorus sorption by natural calcite and the effects of pH and grain size

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.