– Dr Richard Coulton , CEO

and the amount of lime added , gypsum precipitation typically only reduces the sulphate concentration to between 1600mg / l and 2400mg / l , often significantly exceeding the required water quality standard .

Options for reducing the sulphate concentration to below the required standard include : nanofiltration / reverse osmosis , which is limited due to the need to prevent fouling of the membranes and the disposal of the reject waste brine generated ; ionic exchange , which has the same disadvantages ; barium sulphate precipitation , which can achieve very low residual concentrations but is costly ; biological sulphate reduction , which is most effective at an elevated temperature and relies on methanol or another source of carbon to feed the bacteria – it is used on a few applications for metal recovery but has not found favour due to operational costs ; and ettringite precipitation , which elevates the pH of the water using lime and an external aluminium source to form insoluble ettringite – this has attracted interest but is considered costly and operationally complex .

Mine water treatment has come far but meeting stricter discharge standards on potentially toxic metals , and reducing sulphate concentrations , particularly in arid regions , still needs to be addressed . A lot of technology already exists to meet these standards – the challenge is doing this in a way that ’ s affordable to both the mining industry and society as a whole .

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