Characterisation and treatment of soda ash smelting slag from the recycling of lead acid batteries

Soda ash smelting slag from recycling lead acid battery residues can result in serious environmental effects. The slag is very reactive and can cause fires through 'overheating' especially of large pieces of slag; it is also highly alkaline and therefore corrosive. This paper describes a systematic study of the characteristics of slag samples from a lead acid battery recyc ling plant, particularly the heat generation and alkalinity. Methods for th e measurement of 'reaction enthalpy with water' (calorimetry) and soluble a lkalinity (potentiometric titration) of the slag have been developed succes sfully, with both methods having good reproducibility. The chemical composi tion (XRF) and the chemical/mineralogical phases (XRD) of the slag were als o obtained. Experiments suggest that the 'overheating' problem of slag is c aused mainly by its reactions with water. A laboratory-scale treatment proc edure for the slag is proposed where, through a relatively simple and safe procedure, a slag can be processed into a relatively non-hazardous form. Mo reover, the waste water produced from the slag treatment can be used to neu tralise the free waste acid from spent lead acid batteries to produce sodiu m sulphate, a useful chemical byproduct.