Determination of alumina, silica and iron oxide in lateritic soils and kaolins by flow injection analysis

Abstract

The purpose of this research was focused on the determination of alumina, silica and iron oxide in lateritic soils and kaolins by using flow injection analysis in order to get the feasibility, accuracy and precision in analysis. A sample was prepared by fusion with sodium hydroxide and subsequent dissolution of the cake in 1 M hydrochloric acid. Effect of mixing-coil length, sample injection volume, flow rate, reagent concentration and interfering species were investigated. The flow injection system was consisted of one channel which carried the colorimetric reagent solution. The procedure of this approach was illustrated by three speciesa (1) The flow injection analysis procedure was described for the determination of alumina, based on its complex with calcium-alizarin red S. The proposed procedure allowed the determination of aluminium concentrations in the range 3.0-25.0 ppm at a rate up to 120 samples per hour with 1.31% RSD. (2) The determination of iron oxide by the flow injection analysis was based on its complex with ammonium thioglycolate in basic medium. The precipitation of metal hydroxide was prevented by using an onium citrate. This system can operate at up to 180 samples per hour with 2.40% RSD. The working range was 1.0-40.0 ppm of iron (3) The determination of silica was based on the method of yellow silicomolybdic acid. The flow injection system permitted a high sampling rate, up to 120 samples per hour with 1.95% RSD. The working range was 5.00-200 ppm of silicon. These flow injection procedures had been applied to determine these three species in kaolins and lateritic soils of Thailand and gave satisfactory agreement with the classical method.