Sorption of heavy metals from industrial waste water by low-cost mineral silicates

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Abstract
The adsorption by different silicate minerals of some heavy metals, present in industrial waste water, has been studied. These adsorbents (mainly clay minerals) are readily available, inexpensive materials and offer a cost-effective alternative to conventional treatment of wastes from the metal finishing industry. The results show that some mineral species are suitable for the purification of such residual waters down to the limits prescribed by current legislation concerning industrial wastes. The Langmuir model was found to describe such adsorption processes best. Sepiolite (Orera, Spain) has an adsorption capacity of 8.26 mg g-1 for Cd2+, the capacities depending on the metal adsorbed in the order: Cd2+ > Cu2+ > Zn2+ > Ni2+. This mineral shows the highest sorption capacity relative to the other minerals studied. Factors in the reaction medium such as pH and ionic strength influenced the adsorption process.