Be2(OH)2CO3 solubility in carbonate and fluoride aqueous solutions

Abstract

Beryllium is known to precipitate in the form of basic carbonates from neutral and alkaline solutions [1]; the solubility of beryllium basic carbonates is mainly due to the formation of strong hydroxide, carbonate, and mixed-ligand hydroxocarbonate complexes [2‐7]. The thermodynamic properties (solubility products) of basic carbonates and the stability constants of beryllium hydroxocarbonate complexes have not yet been determined with sufficient accuracy. The possible occurrence of strongly bonded fluorocarbonate complexes (they are also poorly studied) adds even more uncertainty to the calculations of beryllium speciation [7]. As a result, the estimation of the environmental mobility of beryllium becomes considerably less reliable, and it is more difficult to develop efficient green technologies. To partially fill in the existing gap, here we report the experimental investigation of CÂ 2 (ec) 2 ee 3 solubilities in carbonate solutions. In the experiments, we used basic beryllium carbonate CÂ 2 (ec) 2 ee 3 , which was precipitated from a boiling 0.05 M BeSO 4 solution with a twofold excess of a heated-to-boil 0.5 M Na 2 CO 3 solution. CÂ 2 (ec) 2 ee 3 solubilities were studied in 0.7 M NaClO 4 solutions that contained variable amounts of Na c CO 3 and Na 2 CO 3 with their overall concentration being less than or equal to 0.05 mol/L. In one set of runs, the solutions in addition contained NaF. The weight ratio of the solid phase to solution in all runs was 1 : 200. The run duration was 2 weeks, which was about twice as long as the period required for the solute beryllium concentration and pH to acquire constant values. The solution temperatures were within 25 ± 1°e . At the end of a run, the sample was filtered through presteamed, fine Blue Ribbon paper filters. The filtrates were colorimetrically analyzed for beryllium using Beryllon II indicator and for carbonate alkalinity using an acidometric method; the filtrate pH was determined potentiometrically. The measurement error was ± 5%, ± 2% , and ± 0.005 pH, respectively. The results of the experiments are displayed in the table. Because the concentration of free Be 2+ ions is ignorable at pH > 8 [2, 6], the CÂ 2 (ec) 2 ee 3 solubility is determined by the concentration of hydroxide, carbonate, and hydroxocarbonate complexes. In view of this, the reaction of CÂ 2 (ec) 2 ee 3 dissolution can in general be written as