Recovery of exhaust magnesium sands: Reclamation plant design and cost analysis

At present about 1200 t/year (the 45% b.w. of the solid waste production) of exhaust sands utilized for moulds and cores in the magnesium casting operations of a foundry plant in Northern Italy are landfilled. In fact, these sands cannot be subjected to the usual process of thermal regeneration because of the presence of potassium fluoborate, a salt which becomes plastic at high temperature values and binds silica grains in close heaps. A dissolution process was tested as a possible solution aimed at recovering both silica sands and potassium fluoborate. Some laboratory tests were performed in order to single out the best operative conditions (dissolution temperature, contact time and solid–liquid ratio) to obtain high quality products and raw water saving. On the ground of the obtained results a full scale plant for the sands reclamation was designed: for this plant the equipments design, the streams evaluation and the costs assessing were performed.