THE SELECTIVE RECOVERY AND CONCENTRATION OF SULFURIC-ACID BY ELECTRODIALYSIS

A process is described wherein sulphuric acid is selectively recovered and concentrated from an acidic nickel sulphate stream containing copper, arsenic, bismuth and antimony in addition to nickel. The process employs electrodialysis (ED), and has been tested at the mini-pilot scale (a 0.2-m2 ED stack supplied by Tokuyama Soda of Japan). Acid extraction rates of 170-450 g m-2 h-1 were achieved depending on the current density applied, resulting in recovered sulphuric acid solutions of up to 280 g H2SO4/1 from a feed containing 150-180 g H2SO4/1, and a total acid recovery of > 80%. Nickel transfer into the recovered acid stream was <10%. Also depending on the current density used, energy requirements were 0.4-5.2 kWh/kg of acid recovered. Data are presented showing that the process is reliable and predictable, and readily amenable to process control. Important parameters, notably the clarity of the feed stream and impurity deportment. are also discussed, and it is shown that the system is a technically viable alternative to other acid recovery systems such as ion exchange and evaporation.