Removal of cupric ion from solution by contact with peanut skins



Certain tannin-containing agricultural wastes, such as peanut skin, are highly efficient ion exchange materials for the removal of cupric ion from aqueous waste solutions. Concentrations of Cu2+ as high as 200–1000 ppm can be reduced to less than 0.5 ppm by pouring the waste solution through a short column of peanut skin. The column packing can take up greater than 10% of its weight in copper, even from 50 ppm solution. Complete regeneration of the packing is readily achieved by eluting the Cu2+ from the column with 0.1 N HCl. The ion exchange process is pH dependent, with optimum removal of copper from solution occuring in the 5–7 pH range. Two hydrogen ions are liberated into solution for each Cu2+ attached to the peanut skin, so pH decreases as reaction continues, inhibiting the reactions. Thus, a continuous column process would be more efficient than a stepwise batch process.