Lead concentrates commercial terms

For a typical lead concentrate, the following gives a calculation of standard commercial terms ... 

These two stages may be within the one smelting site or may be two separate businesses, with crude lead bullion being the traded intermediary. Traded lead bullion is commonly derived from the treatment of primary concentrates, but can also be lead bulUon produced from secondary sources. Secondary bullion generally contains much fewer impurities. As an example, ISF smelters do not usually include lead refining operations and consequently sell their crude lead bullion to a refinery. The commercial terms for the sale of lead bullion are typically as follows ... 

The cost of concentrates. In accordance with Chapter 3 Commercial Terms for Purchase of Standard Lead Concentrates concentrate feed has been costed on the basis of a 60 per cent lead content, 1000 g/t of silver and 3 g/t of gold, and a treatment charge of US 265/t of concentrate at a lead price of US 1100/t, giving a net cost of US 650/t of concentrate. 

These long-term small catchment study results suggest that stream water concentrations are very low and not a water quality concern. In addition, a study of lead in soil solution and stream water following a commercial whole-tree harvest at Hubbard Brook showed that Pb was not released to drainage waters from clearcutting activities (Fuller et al., 1988). 

Batch emulsion polymerizations tend to proceed at high rates because the monomer concentration in the particles achieves an equilibrium value in the presence of excess monomer in the form of droplets and is, therefore, a maximum for arqr given system. Typical rates of polymerization are of the order of mol dm s , which corresponds to approximate heat outputs in the range 0.6-100 J dm s for the most coimnonly used monomers. Hence there is a need for efficient heat removal, a requirement which becomes a serious issue when reactions are performed on an industrial scale. Fra example, simple calculations show that polymerization of 5 tonnes of viiQ l acetate to give a 50% solids latex would result in tqrproximate heat outputs of 500-50000 kJ min at typical rates of batch emulsion polymerization, and would lead to a temperature rise of around 200 C if the reaction were carried out under adiabatic conditions. In these terms, it is easy to tqrpreciate why heat transfer problems provide a further restriction in the use of batch processes on a commercial scale. 

Reliance on native MLF may represent an unpredictable situation, slowing the progress of processing and potentially leading to incomplete conversion of malate. As a result, most winemakers now utilize commercial LAB starters. As with yeasts, LAB starters accomplish the goal of immediate numerical superiority over potentially competitive native strains. Compared with MLF resulting from native strains, properly prepared and expanded inocula of commercial LAB generally yield more predictable results in terms of both the rate of conversion and final concentration of L-malic acid, as well as sensorially active metabolites. 

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