活性硫黄末によるアンモニア性溶液中の銅除去反応における硫黄中間生成物

抄録

Copper (II) in an ammoniacal solution comaining 5 g/dm³Cu and 3 N NH₄OH was eliminated by precipitating CuS ata controlled pH of 10 and at 50°C (323 K) by disproportionation reaction of activated sulphur powder containing isotope 35S. The progress of the elimination was monitored by measuring the suspension potential (SCE). Intermediate sulphur compounds formed during the reaction were identified by means of thin layer radiochromatography and their concentrations were semiquantitatively determined using autoradiogram and a 2πgas flow counter.
The reaction involved were closely related to the suspensionpotential. In the range-0.07 (start)-0.13V, S₄O₆^-2and S₃O₆^-2 (maximum concentration: 0.003 and 0.002 mol/dm³, respectively) were found in the solution, but not SO₂^-4 and S₂O2^-3.An unknown S species, which did not migrate on a plate by development, wasalso found. This S species was considered to be a complex involving the thionate anions. At-0.13 V, S₄O₂^-6and the S species disappeared, S₃O₂^-6decreased, and S2O2-3 appeared. These S₂0₂^-3and S₃0₆^2-were stably present in the solution at constant concentrations (0.028 and 0.0008mol/dm, respedtively) until the suspension potential approached a final value of-0.34V.
It seemed that the precipitation of CuS had no relation to the changes of the sulphur compounds described above. For 4 times of repeated experiments, the precipitation proceeded at a nearly constant rate (0.6g/h), however an induction period was shortened. The precipitation wascompleted at-0.23 V. The following reactions have been considered. Above-0.13 V: 10 Cu (NH₃) ₄²⁺⁺17 S+12 H₂O=10 CuS+S₄O₂^-6+S₃O_2-6+40 NH₃+24 H⁺at-0.13V: 2 S₄O₂^-6+2S+3 H₂O=5 S₂O₂^-3+ 6H⁺2 S₃O₂^-6+4S+3 H₂O=5 S₂O₂^-3+6H⁺and in the range-0.07-0.23 V: 2 Cu (NH₃) ₄²⁺⁺4 S+3 H₂O=2 CuS+S₂O₂^-3+8 NH₃+6H⁺