Cryomagnetic technic for removal of heavy metals ions in effluent treatments

High-gradient magnetic separation can very often offer a solution to the problems of purification of urban and industrial waste water. Two types of application exist: • removal of paramagnetic solid particles in suspension in the effluent treated, • removal of dissolved or ultrafine elements by magnetic seeding (magnetite powder) and coagulation: a variant of this process is the simultaneous precipitation of a hydrated iron oxide, playing the role of a magnetic carrier, with the elements to be removed. The performance offered by high-field/high-gradient magnetic separation has led to the magnetic purification of heavy metals, dissolved or precipitated in colloidal form, in washing effluents from the surface treatment industry, for example. The coprecipitation of a 'magnetic carrier' with heavy metals has been investigated. The mixture of ferrous sulphate and ferric chloride, in basic medium, yields a hydrated magnetite. The initial ratios of divalent ion to trivalent ion range from 0.5 to 1.2. This mixture, coprecipitated with the heavy metals, helps to achieve optimal magnetic purification in a high-field/high-gradient filter. The article describes the filtration superconductor prototype, and gives the main results of magnetic purification obtained on synthetic solutions based on cadmium, zinc, iron etc, and also on industrial fluids.