Ore solution chemistry VI; PbS solubility in bisulfide solutions to 300 degrees C

To evaluate possible bisulfide complexing in ore solutions, galena solubility was measured to 300 degrees C in 0 to 2.85 m NaHS solutions at H (sub 2) S pressures of 0.8 to 75 atm. A maximum solubility of 47 ppm PbS was found in 0.5 m NaHS solution at P (sub H (sub 2) S) = 75 atm, 300 degrees C. Derived from these solubilities were stoichiometries and thermodynamic stability constants for the dominant complexes. At temperatures where each complex is important, log K is: degrees C: 30 50 100 200 300(1) PbS+H (sub 2) S(g)+HS (super -) <-->Pb(HS) (super -) (sub 3) -6.6+ or -0.2 -6.7+ or -0.2 -6.9+ or -0.2(2) PbS+H (sub 2) S(g)<-->Pb(HS) (sub 2) (aq) -7.8+ or -0.2 -6.6+ or -0.2 -6.4+ or -0.2 -6.4+ or -0.2(3) PbS+2H (sub 2) S(g)<-->Pb(HS) (sub 2) (H (sub 2) S)(aq) -8.0+ or -0.2 -7.2+ or -0.2Apparently, sulfide complexing of lead may be important for ore transport only in exceptionally sulfide rich solutions and, above 250 degrees C, the solution must also be geologically improbably alkaline.