西宁降尘的柠檬酸酸溶特性研究

Dissolution Characteristic of Dustfall in Citric Acid from Xining, China

以西宁降尘为研究对象,探讨柠檬酸溶解2 d过程中体系的pH及电导率变化,借助XRD、FTIR、SEM和ICP等表征手段,对降尘经酸处理后的残余固体及上清液进行分析。降尘加入柠檬酸的前4 h,反应溶液pH迅速上升;电导率从初始的4.31 ms/cm迅速升高到5.61 ms/cm,然后缓慢下降;8 h后,pH和电导率基本达到稳定。根据XRD分析,白云石特征峰(d=0.2886 nm、0.2190 nm等)和方解石特征峰(d=0.3031nm、0.2282 nm等)完全消失;根据红外分析,代表碳酸盐矿物的特征峰(1430 cm-1和877 cm-1)也消失,结合XRD结果可以得出方解石和白云石在柠檬酸作用2 d后完全溶解。柠檬酸溶出了降尘中大量的Ca2+,K+,Mg2+,Fe3+,Al3+,Si等元素,其中Ca2+的溶出量达到711.63 mg/L。柠檬酸对不同元素溶出的促进作用由强到弱依次为:Fe>Al>Si>Ca>Mg>K。在柠檬酸的作用下,降尘中的矿物被全部或部分溶解,其中碳酸盐矿物几乎完全溶解。

pH and conductivity was tested during dissolution process for Xining dustfall in citric acid to evaluate changes of reaction solution. After 2 days＇ dissolution, SEM, FTIR, SEM and ICP analysis method was applied to analyze the residual solid and filtrate. PH of reaction solution increased fast in 4 hours, and conductivity sharply increases from initial 4.31 ms/cm to 5.61 ms/cm in 1 minute after addition of dustfall, then followed a slowing down stage. After 4 hours, both the pH and conductivity become stable. Based on comparatively analyzing of XRD for dustfall and residual solid, characteristic peak of calcite （e.g. 20=-30.986°, 41.182°） and dolomite （e.g. 20=-29.455°, 39.507°） are disappeared. Similar results can be seen from FTIR analysis, with absorption peak （1430 cmland 877cm-1） of carbonate minerals disappeared. Combined above two analysis results, we can demonstrate that calcite and dolomite in dustfall are dissolved in the 0.5 mol/L citric acid solution. Amount of metal cations including Ca2＋, K＋, Mg2＋, Fe3＋, A13＋ and Si are extracted from dustfall during the dissolution, of which the dissolution quantity of Ca reached 711.63 mg/L. Compared with dissolution in distilled water, effect of citric acid on different elements can be rank as follow： Fe〉Al〉Si〉Ca〉Mg〉K. After dissolved in 0.5 mol/L citric acid, some minerals in dustfall disappear and amount of metal elements are extracted, especially the carbonate minerals almost dissolved completely, and structure of silicate minerals changed as the extraction of elements.