Behaviour of sepiolite in Co2+ Cu2+ and Cd2+ removal from a simulated pollutant solution

The present study reports on the ability of sepiolite, a hydrous magnesium silicate mineral, to remove metal ions from simulated industrial wastewaters. Fixed beds (weight = 50 g, grain size = 0.30-0.60 mm) of sepiolite from Vallecas (Spain) were percolated by gravity with Co2+, Cu2+ and Cd2+ meta solutions at constant ionic strength. Sepiolite was used both in its natural state and after repeated treatments with Mg2+ solutions at increasing concentrations (10-2N, 5x10-2N, 10-1N). The cation breakthrough and elution curves show that: i) sepiolite beds retain the heavy metals in question in the following order Cd2+ ? Co2+ < Cu2+; ii) Ca2+ and Mg2+ are the cations most readily released by untreated beds; iii) after regeneration, the ability of the beds to retain heavy metals is only slightly reduced. X-ray powder diffraction patterns, obtained over a wide temperature range (25°-400°C) and differential thermal analyses results obtained on samples treated with heavy metals are only slightly different from those obtained on natural sepiolite, which suggests that the heavy metals do not significantly affect the layer features.