Decoppering additives

Decoppering additives used to decrease the buildup of copper residues in the barrel rifling include tin metal and compounds such as tin dioxide bismuth metal and compounds such as bismuth trioxide, bismuth subcarbonate, bismuth nitrate, bismuth antimonide. The bismuth compounds are... 

One of the most recent uses for Pb is the addition, in the form of foil or coil of wire, to propint pdr as a decoppering agent for the bore of the gun. The Pb is placed between the pro-pint charge and the projectile... 

If a decoppering agent is used for treatment, the compliance can be tested by repeated measurements of the 24 h urinary copper excretion. This approach is not useful if patients are treated with zinc. The dose of d-penicillamine can be lowered if in a compliant patient urinary copper excretion decreases over time and stabilizes at < 500 p g/day. Efficacy of treatment can be monitored by the determination of free copper in serum, and depending on the presenting symptoms. Liver disease can be assessed by routine liver function tests. Repeated liver biopsies with measurement of hepatic copper content are not helpful. Improvement of neurological symptoms can be documented by clinical examination or by auditory evoked brainstem potentials. In addition, some of the MRI abnormalities are fully reversible on treatment. 

Figure 3 shows the results of tests conducted to determine the amounts of silver or tin required to ensure that lead can be decoppered with sulfur to around 0.0015 Cu, at 330 C, within about 10 minutes. The lead contained about 0.05% Cu initially, and varying amounts of tin or silver, but no significant amoimts of other impurities. Increments of 0.02% S were added each minute, and lead samples were taken after 5 minutes and after 10 minutes. It will be noted that 0.02% Ag suflices to permit 0.1% sulhir to decopper to 0.001% Cu, even within 5 minutes, and the results are not significantly different for higher amounts of silver. Sn behaves differently. With 0.05 % Sn present, 0.001% Cu is reached after 10 minutes stirring, and a total addition of 0.2% S. On the other hand, 0.001% Cu is reached with 0.10% Sn after 5 minutes stirring, and the addition of 0.1% S in total. 

When no silver or tin is present, repeated additions of sulfur alone produce some decoppering, but the PbS fonnation is excessive, and the procedure has no commercial significance. 

B.S. Terry, C.L. Harris and D.G.C. Robertson, The Decoppering of Liquid Lead Bullion by Elemental Sulphur Additions, Part 1 The Sulphidation of Lead by Elemental Sulphur. Trans. I.M.M.. 102,1993, C57-C62. 

Figure 12.3 suggests that the copper level in lead cannot be reduced below the equilibrium solubility of around 0.06 per cent by sulfur addition (or down to 0.02 per cent if arsenic or antimony are present), whereas in practice it is possible to go an order of magnitude below this to 0.001 to 0.005 per cent copper. It has been found that these levels cannot be reached in the absence of silver or tin, which act as promoters of the decoppering reactions. A percentage of 0.002 silver is required to achieve copper levels of around 0.001 per cent (Davey and Happ, 1971). It has also been found that continued stirring of the dross with decoppered bullion can cause the copper to revert and redissolve into the bullion. The explanation for this phenomenon lies in the fact that the reactions are controlled by kinetics and not thermodynamic equilibrium. 

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