碱熔-硫酸铁铵滴定法测定钛白粉中二氧化钛

二氧化钛的含量决定了钛白粉产品质量等级,准确测定钛白粉中二氧化钛含量具有重要意义。采用过氧化钠高温熔融样品,热水浸取,盐硫混酸溶解,用铝箔将溶液中四价钛还原为三价,在饱和碳酸氢钠溶液的保护下以硫氰酸铵为指示剂,实现了硫酸铁铵滴定法对钛白粉中二氧化钛含量的测定。讨论了样品分解方法、过氧化钠用量、盐硫混酸用量对测定结果的影响。结果表明,将0.200 0 g样品置于盛有2.000 g过氧化钠的30 mL刚玉坩埚中,在样品上铺1.000 g过氧化钠,先在马弗炉中500 ℃低温熔融5 min,待过氧化钠固体融化后再升温至650 ℃继续熔融10 min,加入30 mL热水浸取,再缓慢加入30 mL盐硫混酸,可将熔融物全部溶解。按照实验方法对钛白粉标准物质和样品进行测定,标准物质的测定结果相对误差小于《地质矿产实验室测试质量管理规范》规定的相对误差允许限,样品测定结果的相对标准偏差(RSD,n=6)小于0.2%。

Determination of titanium dioxide in titanium pigment by ammonium ferric sulfate titrimetry with alkali fusion

The content of titanium dioxide determines the quality grade of titanium pigment products, so the accurate determination of titanium dioxide content in titanium pigment is of great significance. The samples were melted by sodium peroxide at high temperature. Then it was leached by hot water followed by dissolution with mixed acid composed of hydrochloric acid and sulfuric acid. The quadrivalent titanium in solution was reduced to trivalent with aluminum foil. Under the protection of saturated sodium bicarbonate solution, the content of titanium dioxide in titanium pigment was determined by ammonium ferric sulfate titrimetry with smmonium thiocyanate as indicator. The effects of sample decomposition method, the dosage of sodium peroxide, and the dosage of mixed acid composed of sulfuric acid and hydrochloric acid on the determination results were studied. The results showed that the sample could be fully dissolved under the following conditions: 0.200 0 g of sample was transferred in a 30 mL corundum crucible containing 2.000 g of sodium peroxide; the sample was covered with 1.000 g of sodium peroxide; the mixture was melted in muffle furnace at 500 ℃ for 5 min; when the solid sodium peroxide was melted, the temperature was increased to 650 ℃ for further melting for 10 min; 30 mL of hot water was added for leaching; finally, 30 mL of mixed acid composed of hydrochloric acid and sulfuric acid was added slowly to dissolve the melt. The certified reference material and actual sample of titanium pigment were determined according to the experimental method. The relative error of the determination results for the certified reference material was less than the allowable limits of relative errors stipulated in The specification of testing quality management for geological laboratories. The relative standard deviation (RSD, n=6) of determination results of actual sample was less than 0.2%.