Al-rich sludge treatments towards recycling

A treatment method towards recycling of Al-rich sludges to produce high-alumina refractory ceramics is proposed. These sludges are collected in wastewater treatment units of industrial plants dealing with anodising or surface coating processes. This industrial residue usually contains significant amounts of soluble salts such as Na, K, Mg, Ca and Al sulphates that make direct recycling problematic. The removal of these salts from the as-received sludges by washing is ineffective due to its gel-like consistency. The treatment consists of calcining and subsequent washing operations, followed by removal of sulphates by precipitation as BaSO4. The treated sludges could then be well dispersed and processed by slip casting.