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.