Solubility of Gibbsite ( Alpha - A1(OH) Sub 3 ) in 1 Molal NaCl as a Function of pH and Temperature

摘要

Discussed are the advantages and disadvantages of the column approach to study the pH dependence of the solubility of well crystallized hydroxides, and preliminary results on gibbsite (Al(OH) sub 3 ) are presented. Good results have been obtained in the basic region, and the temperature dependence of the equilibrium quotient for the reaction Al(OH) sub 3 (c) + OH exp - reversible Al(OH) sub 4- in lM NaCl is given by log Q/sub s14//sup b/ = 3.3766 - 1326.4/T with an agreement factor of 0.035 (unit weights). These measurements were made over the temperature range 35 to 90 exp 0 C at the base concentrations of 0.01 M and 0.1 M NaOH. The principal difficulty with the column approach is the strong buffering capacity of the column itself for equilibrations in the near neutral pH region. We found that the capacity could be accounted for in terms of monolayer adsorption (or reaction) of H exp + ions. Although insufficient evidence for equilibrium was obtained, data in the pH range 3 to 4 give the value of -7.20 +- 0.15 at 60 exp 0 C for the log Q/sub s10/ for the reaction Al(OH) sub 3 (c) + 3H exp + reversible Al exp 3+ + H sub 2 O. Results of solubility measurements in the near neutral region are preliminary. 8 figures, 4 tables. (ERA citation 05:013982)