Preparation of polymeric aluminum chloride from secondary aluminum dross and its water purification effect

Aluminum dross is solid waste generated by the aluminum industry. Currently, a large amount of aluminum dross is produced annually year. Aluminum dross, a hazardous waste, contains harmful substances such as aluminum metal, aluminum nitride, fluoride and chlorine salts, which pose a serious threat to human health and also cause damage to the ecological environment. Thus, it is important to recycle secondary aluminum dross and realise its high-value utilisation. Polymeric aluminum chloride (PAC) is a polymer flocculant, at present, China's annual use of PAC in the field of water treatment is about 5 × 105 t, and with the continuous improvement of water purification requirements, the annual use of PAC increased year by year. Here secondary aluminum dross was used as a raw material to prepare PAC by hydrochloric acid (HCl) leaching, followed by the addition of sodium carbonate. The optimal conditions for the acid leaching of secondary aluminum dross for the preparation of PAC were as follows: HCl concentration, 18%; liquid-to-solid ratio, 4.5:1; stirring rate, 200 r/min; reaction temperature, 90 °C; and 60 min. An aluminum leaching rate of 85.5% was obtained under these conditions. The results showed that the acid leachate after adding sodium carbonate, under the conditions of polymerisation temperature of 70 °C, polymerisation time of 6 h, and polymerisation pH value of 3.0, the PAC prepared had an alumina content of 10.19%, salinity of 32.37%, density of 1.32 g/cm3, 1% aqueous solution pH 4.3. The water purification effect of the prepared PAC surpassed that of the commercially available PAC. The utilisation of secondary aluminum dross can reduce the environmental pollution caused by aluminum slag.