Catalysis and synergism in the reduction smelting of lead sulfide with carbon and lime

Abstract

The catalyzed direct reduction of lead sulfide with carbon and lime was investigated at several temperatures and under two different inert gas atmospheres. The catalyzed reduction kinetics were determined both with a nitrogen atmosphere and a helium-rich helium-nitrogen atmosphere. The reduction kinetics under the latter were decidedly superior to those under the former. The differences were interpreted in terms of faster diffusion rates in a helium medium and synergistic effects. The catalyst used was a ternay eutectic mixture (K, Li, NahC03, which amounted to 2.5 wt. SCOPEThe effect of ambient atmosphere and the influence of temperature on the reduction smelting of lead sulfide with carbon and lime have been investigated in the temperature range 1,061 to 1,262 K. The experimental data are analyzed by means of a physicochemical model that envisions the Boudouard reaction (C + Cog -+ 2CO) as the rate-controlling step for the overall reduction process. The intrinsic rate constant values were derived by the application of the model. The rate constant values for reduction under helium-rich helium-nitrogen atmospheres are systematically higher than those for reduction under nitrogen atmospheres. These differences were reconciled in terms of synergistc effects arising from the presence of the catalyst. CONCLUSIONS AND SIGNIFICANCEThe addition of the ternary eutectic catalyst (K, Li, NahCOs proved to be quite effective in promoting the reduction rates in the PbS:4CaO:4C mixtures in the temperature range 1,061 to 1,262 K. The catalyst was added in modest amounts, i.e., 2.5 wt. %, and is known to exist in a molten state at all the temperatures investigated. The extent of catalysis was found to be significantly influenced by the nature of the inert ambient atmosphere used. The reaction mechanism consisted of reduction, carbon gasification, and PbS vaporization steps with the middle step constituting the rate-limiting phenomenon. The intrinsic rate constant values for carbon gasification were obtained for two different atmospheres: log 11 = 5.300 -8,480 T-' for heliumrich helium-nitrogen atmospheres and log 11 = 3.981 -7,790 T-' for nitrogen atmospheres. The catalyst addition in conjunction with the ambient atmosphere, eyen.though the latter is inert, produces a synergistic effect; that is, the catalyst is more effective in a helium-rich helium-nitrogen atmosphere as compared to a nitrogen atmosphere. This synergistic effect, expressed as a ratio of the intrinsic rate constants, has a value of 4.7 at 8OO0C, which rises to 6.0 at l,OOO°C.

Recovering Zn, Pb, Cd and Fe from electric furnace dust

“…8 Although Li 2 C0 3 produces the most favorable catalytic results, Na 2 C0 3 produces similar results at greater economy (Table III, tests 6 and 7). A 99% recovery of zinc, an upgraded zinc product containing 90.3% zinc and a metal residue containing 56% iron were Samples of EFD received from one company in two separate batches (2093A and 2093B, collected in January and June of 1987, respectively) were analyzed chemically and by x-ray diffraction.…”