地热水中高浓度硅酸盐自动测定方法及系统的研究

Study on Automatic Determination Method and System of High-concentration Silicate in Geothermal Water

根据地热水中高浓度硅酸盐含量、调节硅垢抑制剂的添加量,可防止地热发电废水回补管道中硅酸盐的结垢。所以,开发了一种自动测定高浓度硅酸盐的新系统。地热水样在流路中与NaOH溶液混合、反应（使聚合硅转化成活性硅）后,进入样品定量环自动定量,此时显色剂也同时定量;然后,同时被注入到载流中,以合并带中试剂包裹试样方式进行汇合、反应;生成的产物经过干扰消除盘管掩蔽干扰物后,进入流通检测器在405 nm波长下进行定量。优化的测定条件为：钼酸铵浓度为2%（w/v）,NaOH浓度为0.1 mol.L-1;草酸浓度为1.0%,预混合盘管长度为350 cm,反应盘管长度510 cm,干扰消除盘管长度为300 cm,载流流量为5.0 ml.min-1;该方法每次测定所需的样品用量仅为25μl,显色剂用量仅为120μl,测定范围为25~800 mg.L-1（SiO2）,相对标准偏差小于0.81%,回收率为96.2%~117.0%,分析速度为180个样.h-1;该系统的特点是重现性好、分析速度快、测定成本极低,高浓度硅酸盐测定时无需预稀释处理、自动化程度高,可用于地热水中高浓度硅酸盐的监测。

Based on the silicate content in geothermal water,adjusting the addition amount of scale inhibitors can prevent the formation of silicate scale on the surface of returning pipes in the deep underground.Consequently,an automatic system for determining the high-concentration silicate was proposed.This analytical process was as follows.First,NaOH solution mixed with a sample of geothermal water in premixing coil to make polymeric silicon translate into active silicon like H4SiO4 and SiO32-.And then volumes of the sample and a chromogenic agent were measured simultaneously and automatically,injected into two carriers,merged and reacted in a reaction coil in manner of the reagent enwrapping the sample.Formed product entered into a masking coil of eliminating interferences and a flow detector in turn,and was determined under the wavelength of 405 nm.Optimized conditions were as follows： Concentrations of ammonium molybdate,NaOH and oxalic acid were 2%（w/v）,0.1 mol·L-1,and 1%（w/v）,respectively,lengths of premixing,reacting and masking coils were 350,510,and 300 cm,respectively;the total flow rate was 5.0 ml· min-1.This method only consume 25 μl of the sample and 115 μl of the chromogenic reagent per time,its determination range was 25~800 mg·L-1（SiO2）,relative standard deviation was less than 0.81%,recovery ranges were 96.2%~117.0%,about 180 samples can be analyzed per hour.Merits of the system were good reproducibility,high analysis speed,less test-cost,and not needing to predilution for determination of high concentrations silicate.The most important was that it realized continually monitoring of the high concentration of silicate in the geothermal water.