Surface Chemistry Aspects of Ion Exchange in Basic Copper Salts

Brochantite was precipitated using stoichiometric amounts of CuSO₄ and NaOH and characterized by scanning electron microscopy, specific surface area, thermogravimetric analysis, and zeta potential. Brochantite can be converted into paratacamite, basic copper bromide, and copper phthalate by shaking the powder with solutions containing excess corresponding anions. By contrast, attempts to convert brochantite into basic iodide, acetate, nitrate, or rhodanide in a similar way failed, that is, the powder after shaking with solutions containing excess corresponding anions still showed the powder X-ray diffraction pattern of brochantite. Successful ion exchange resulted in a decrease in the specific surface area by a factor of 10, but the specific surface area was unchanged when attempts to exchange the anion failed. Interestingly enough, paratacamite can also be converted into brochantite by shaking with solution containing excess sulfate. Brochantite and paratacamite obtained by precipitation and the salts obtained by ion exchange showed a negative zeta potential at pH > 9.