Adsorption of Microamounts of Silver on Manganese Dioxide from Acid Solutions

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Abstract
Adsorption of microamounts of silver on manganese dioxide from nitric and perchloric acid solutions has been studied and optimized with respect to shaking time, concentrations of electrolyte, adsorbent, and adsorbate. Maximum adsorp- tion (>99.5%) has been achieved from 0.01 mol/dm3 acid solution using 50 mg oxide at 10−5 mol/dm3 silver concentration after 30 min shaking. The adsorption decreases with increasing concentration of acid and adsorbate from both the acids. The presence of a 104-fold greater concentration of cyanide, thiocyanate, thiosulfate, and Pb(II) than silver reduces the adsorption drastically. The adsorption of silver follows the Freundlich adsorption isotherm over the entire concentration range investigated from 9.27 × 10−6 to 2.92 × 10−3 mol/dm3 with a value of A = 49 mmol/g and 1/n = 0.93. Moreover, the Langmuir adsorption isotherm is also valid except at the lowest and highest concentrations. The values of the limiting adsorption concentrtion (Cm ) have been found to be 1 mmol/g and of the equilibrium constant for adsorption 87 dm3/mol at 23 ± 2°C.