超声萃取-硝酸汞滴定法测定石英砂岩中氯离子

鉴于硝酸银滴定法测定岩石矿样中氯离子的前处理方式一般采取去离子水浸泡、振荡萃取、过滤等,操作手续冗长,易污染,难过滤的特点,实验研究了超声萃取-硝酸汞滴定法测定石英砂岩中氯离子的方法。即通过对国家标准岩石样品GBW07106进行超声萃取、静置、然后离心分离,用硝酸汞滴定法测定离心液中的氯离子含量,进而计算出石英砂岩中的氯含量。通过试验确定了对样品进行超声萃取2h、以硫酸铝钾为萃取剂、萃取时间为30min和离心分离时间为10min的前处理方案。对大于10mg/L铬酸盐和大于140mg/L Fe³⁺对Cl^-测定的干扰,可加入2mL 100g/L对苯二酚溶液消除;对大于10mg/L硫化物和亚硫酸盐的干扰,可先用氢氧化钠调节溶液至弱碱性,然后加入1mL 30%过氧化氢摇匀,再加热除去剩余过氧化氢的方法消除其对Cl^-测定的干扰。采用实验方法对石英砂岩进行测定,结果的相对标准偏差(RSD,n=5)为5.5%和6.2%,回收率为97%~103%。

Determination of chloride ion in quartz sandstone by mercury nitrate titration with ultrasonic extraction

During the determination of chlorine ion in rock ore sample by mercury nitrate titration method, the pretreatment usually includes many steps such as deionized water soaking, oscillation extraction and filtration. The operation procedures are long, and the samples are easily polluted and hardly filtrated. The determination of chlorine ion in quartz sandstone by ultrasonic extraction-mercury nitrate titration method was studied. The national standard rock sample GBW07106 was treated by ultrasonic extraction, standing and centrifugal separation. The content of chlorine ion in centrifugate was determined by mercury nitrate titration. Then the content of chlorine in quartz sandstone could be calculated. The following pretreatment conditions were obtained by experiments: the sample was treated by ultrasonic extraction for 2h; aluminum potassium sulfate was employed as the extraction agent; the extraction time was 30min; the centrifugal separation time was 10min. The interference of chromate (＞10mg/L) and Fe³⁺ (＞140mg/L) could be eliminated by adding 2mL of 100g/L hydroquinone solution. For the interference of sulfide and sulfite (＞10mg/L), the solution was firstly adjusted to alkalescence using sodium hydroxide followed by adding 1mL of 30% hydrogen peroxide. After shaking, the residual hydrogen peroxide was removed by heating to eliminate its interference to the determination of Cl^-. The proposed method was applied for the determination of quartz sandstone. The relative standard deviation (RSD, n=5) of results was 5.5% and 6.2%, respectively. The recoveries were between 97% and 103%.