Abstract
Rapid industrialisation is contributing to water pollution. There is a need to identify cheaper and efficient methods of removing contaminants as the demand for clean water rises. A study is carried out to investigate the extraction of alum from locally abundant kaolin clays using sulphuric acid. Alum is a coagulant that is used for raw water treatment. The kaolin clay and alum were characterized by Fourier transformation infrared spectroscopy (FTIR). The effects of particle size, calcination temperature, calcination time, acid-kaolin clay ratio, acid concentration, leaching temperature, and leaching time on extraction efficiency were investigated. The optimum leaching conditions for the calcined kaolin clay were found to be particle size 100 µm, acid-kaolin clay weight ratio 6 : 1, acid concentration 4 M, leaching temperature 100°C, and leaching time 90 min. Under optimised conditions, 66.95% (w/w) aluminum sulphate was extracted. The results showed that sulphuric acid could be used on a large scale to extract alum from kaolin clay. The extracted alum showed similar structural and physical characteristics compared with commercial alum. A dosage of 40 mg/L of the extracted alum showed effective coagulant properties with a great potential of treating raw water.
Highlights
Alum is a coagulant that is used in water treatment plants for supply of safe domestic and industrial water [1,2,3,4]
This study focuses on determining the feasibility of leaching aluminum from locally abundant Zimbabwean kaolin clays using sulphuric acid
Aluminum oxide and silicon dioxide were the major components of kaolin
Summary
Alum (aluminum sulphate) is a coagulant that is used in water treatment plants for supply of safe domestic and industrial water [1,2,3,4]. Alum is traditionally extracted from bauxite, an aluminosilicate mineral by the Bayer process [5]. During this process, the ground bauxite mineral is pressure leached with an alkali such as sodium hydroxide to obtain an aluminate solution. Pure aluminum hydroxide is precipitated from the aluminate solution by seeding. Another aluminosilicate mineral is kaolin which is found among different types of clays [6, 7]. Kaolin is a naturally hydrated aluminum silicate mineral that has a variety of colours ranging from white to red due to presence of variable amounts of iron oxide [8]
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