磷酸盐对石灰岩溶解作用的影响研究

Study on the effect of phosphate on the dissolution of limestones

随着化肥大量的使用,大量磷酸盐下渗到地下水系统中,其可以吸附到方解石族岩石表面(本实验选取石灰岩),对其溶解过程产生影响,从而对碳酸盐岩固碳增汇产生较大影响,前人大多在宏观上分析施肥对碳酸盐岩溶解的影响,而关于施肥中产生的磷酸盐对碳酸盐岩溶解的微观机理研究少之又少,因此本研究对实验中的水化学参数进行测定并论述其可能的反应过程,同时使用场发射扫描电镜(SEM),XRD等多种表征工具对实验后的石灰岩表面进行检测。在2 mg/L和100 mg/L的磷酸盐溶液中反应12 d后,磷酸盐在石灰岩上吸附效果较为显著,石灰岩表面生成的沉淀主要有CaHPO_(4)和少量Mg_(2)PO_(4)(OH),根据扫描电镜图像,石灰岩在低浓度磷酸盐溶液中表面呈现出较为明显的裂缝和溶蚀台阶,在高浓度磷酸盐溶液中呈现为大量不规则蚀刻坑、孔隙和簇状结构,随着水岩化学反应和物理吸附的共同作用,在石灰岩表面形成了金属-磷相沉淀,对石灰岩溶解起到了促进作用。虽然许多研究表明石灰岩可以作为磷酸盐等污染物的吸附剂使用,但是高浓度磷酸盐会加剧石灰岩的溶解作用,其对碳酸盐岩固碳增汇将产生不利影响。

With the massive use of chemical fertilizers,a large amount of phosphate seeps down into the groundwater system,where it can adsorb onto the surface of calcite family rocks(limestone was selected for this experiment)and have an impact on their dissolution process,thus having a greater impact on carbon sequestration and sink enhancement in carbonate rocks,Most of the previous researchers analyzed the effect of fertilizer application on carbonate rock dissolution on a macroscopic level,while there are few studies on the micro-mechanisms of the phosphate generated from fertilizer application on carbonate rock dissolution,therefore,in this study,we determined the experimental hydro-chemical parameters and discussed the possible reaction processes,and also examined the post-experimental limestone surfaces using a variety of characterization tools,such as field emission scanning electron microscopy(SEM),XRD,and so on.Phosphate adsorption on limestone was more significant after 12 d of reaction in 2 mg/L and 100 mg/L phosphate solutions,CaHPO_(4)and a small amount of Mg_(2)PO_(4)(OH)are deposited on the limestone surface,according to the scanning electron microscope image,the surface of limestone showed obvious cracks and dissolution steps in low concentration phosphate solution,and showed a large number of irregular etched pits,pores and cluster structures in high concentration phosphate solution,with the joint action of water-rock chemical reaction and physical adsorption,metal-phosphorus phase precipitation is formed on the limestone surface,which promotes the dissolution of limestone.Although many studies have shown that limestone can be used as an adsorbent for pollutants such as phosphate,the high concentration of phosphate will aggravate the dissolution of limestone,which will adversely affect the carbon sequestration of carbonate rocks.