Preparation and coagulation performance of solid aluminium formate

Abstract

A simple method for the preparation of an aluminium formate coagulant in solid form was developed. Aluminium hydroxide and formic acid were used as starting materials. The effect of different ratios of the starting materials in the synthesis was investigated with a view to minimising the required amount of formic acid. The coagulation performance of the products obtained was evaluated in surface water treatment and aluminium sulphate was used as reference coagulant. Most of the prepared aluminium formates were found to be at least equally effective as aluminium sulphate at optimum coagulation conditions. It was found that relatively small amounts of formic acid are adequate to obtain a well-functioning product. Removal efficiencies of obtained aluminium formates were found to be dependent on coagulation condition, namely coagulant dose and pH. In most conditions, aluminium formate had a similar coagulation efficiency to that of aluminium sulphate. Especially at low pH range, higher removal efficiencies were obtained with aluminium formate than with aluminium sulphate, whereas around pH 5 with high dosages aluminium sulphate was more effective. The prepared aluminium formate coagulants are potential alternatives to commonly used coagulants, especially in applications where chloride and sulphate are problematic due to corrosion or formation of precipitates. The solid form of the coagulant offers some practical benefits over a similar liquid product.