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A process is described which enables the removal of sulphuric acid from effluents without the addition of chemicals to the effluent. The technique employs an anion selective membrane which separates the acidic effluent from a lime solution. In the case where no current is applied, facilitated transport occurs and the driving force for the demineralisation process is the difference in the chemical potential of the species on either side of the membrane. The equilibrium position may be shifted by the passage of a current through the membrane, in which instance the driving force becomes the applied electric potential. The sulphates are removed as calcium sulphate, which precipitates in the lime solution. The specific membrane area reauirements are a function of the desired dearee of acid reduction. The application of -low current densities (500 A/ms) reduces -the specific membrane area requirements for a particular duty by two orders of magnitude compared to facilitated transport. Results of laboratory investigations are given and indicate that the sulphuric acid component can be removed from waste waters without an undesirable build-up of additional dissolved solids.

Laboratory results have indicated that the proposed membrane process is effective in removing the sulphuric acid from industrial and mining waste streams containing the acid. The proposed method has the advantage over conventional treatment methods in that the acid stream is neutralised and demineralised without the addition of further salts to the main effluent stream. The sulphate ions are removed from the effluent and immobilised by precipitation as calcium sulphate in a low volume recirculating saturated lime solution. Where suitable facilities exist for handling oxygen and, in particularly hydrogen gas streams, the use of the electrolysis option is advantageous over the facilitated transport option, since membrane area requirements may be reduced by at least two orders of magnitude. FUTURE DEVELOPMENTS A pilot plant study is to be conducted to assess the feasibility of the process to large scale applications and to obtain suitable data for the design of a full scale plant.