Glass sand processing by oxalic acid leaching and photocatalytic effluent treatment

As part of an EC programme oxalic acid leaching technology has been studied on the pilot scale to reduce the iron content of the silica sand for use in the production of clear flat glass. Heated sulphuric acid is usually employed for this purpose causing environmental problems with neutralisation and discharge of leachate effluents. The primary advantage of using oxalic acids is in formation during leaching of soluble complexes (e.g., trisoxalatoiron(III) anions) which are both photochemically and microbiologically degradable. per outlines pilot scale operations which have been developed to prepare and leach sand in heaps or stirred tanks and to detoxify and utilise the effluents. These operations are unusual in applying a relatively expensive leach reagent at high solid—liquid ratio to remove surface deposits from a bulk industrial mineral, and to make use of sunlight and/or microbial activity to facilitate safe recycle or discharge of process water. Emphasis is placed on the photocatalytic processes employed, particularly the precipitation of crystalline iron(II) oxalate. Calcination of this oxalate is outlined as a possible route to added-value iron products.