Vacuum dezincing

Grades purer than the Prime Western product have been made by vacuum dezincing the Hquid alloy to recover 99.9% zinc at 0.02% lead. Distillation (New Jersey Zinc process) produces a purer product at a considerable cost in energy. 

Method Vacuum Dezlndrig Vacuum Dezincing Vacuum Dezincina > KUum Dezincing Vacuum Dezincing... 

P.R.M. Van Negen and P. Weertes, Vacuum Dezincing of Parkes Triple Alloy in an Induction Furnace , Electric Furnace Techniques in Metallurgy. Bad Salzdetfurth, 19-20 March, 1987,169-176. 

It is often important in the study of a process to determine whether the limitations are governed by equilibrium or kinetic considerations. Sometimes it is possible to devise a design of the process or the equipment so that the apparent limitations set by equilibrium considerations are overcome. In this paper, detailed consideration is given to the lead refining processes of sulftir-decoppering and of vacuum dezincing to illustrate this, and possible implications for other refining processes are indicated. 

When apparently only one reaction is to occur, it may still be of advantage to cause a second reaction to take place, so as to produce a more favorable outcome. This is not necessarily done by introducing additional reagents, but can possibly be done by suitable design of the reaction vessel. This is the case for the removal and recovery of zinc finm lead after the desilverising operation. The bperation is performed under vacuum, so that it will proceed at reasonable speed at relatively low temperatures, and is known as vacuum dezincing. 

Figure S - Batch Vacuum Dezincing Plant, as at St. Joe, Herculaneum, See Reference (34) The Distance Between the Evaporating and Condensing Surfaces is About 30 cm A Mechanical Vacuum Pump Produces a Residual Pressure of About 30 Microns Hg A Lead Temperature of 600°C and Stirring Time of 5 hours Reduced Zinc rom 0.56% to 0.05% Zn in the Dezinced Lead.

Figure 6(b) - Continuous Vacuum Dezincing Plant With Liquid Zinc Condenser,... 

Figure 6(a) - (Semi)-Continuous Vacuum Dezincing Plant at B.H.A.S. Port Pirie,... 

There have been many theoretical determinations of the rates of distillation under vacuum, but none that appeared to be applicable to vacuum dezincing when its development was commenced at Port Pirie in 1946. Thus it was felt to be desirable to develop the theoretical side (37) simultaneously with the practical development, as a guide to understanding and possible later application to optimising of the process. Figure 7 illustrates the concept of the distillation process which was developed. It was necessary to discard some faulty ideas or misconceptions, which derived fix>m implicit notions associated with equilibrium, but not kinetic conditions. Carman (38), for example, assumed that the partial pressure of the vapour of the condensing species is equal to its partial pressure in the condenser. It is not, unless the condensation rate is zero. Richardson (6) assumed that the measured vacuum is equal to the distilling species, which it is not, but is instead the partial pressure of the inert atmosphere. Warner (40) assumed the partial pressure of zinc to be constant across the distillation space, which is not correct unless the distillation rate is zero. 

N.A. Warner, Kinetics of Vacuum Dezincing , Symposium on Advances in Extractive Metallurgy. London, Instn. of Min. and Met., London, 1967,317-332. 

C.F. Harris, J.F. Castle and J. McNish, Vacuum Dezincing , I.S.P. Conference 1967. Imperial Smelting Corporation, London, 1967,852-887. 

Remaining copper and other impurities were originally removed by the addition of zinc, and the removal of zinc was by chlorine to form a zinc chloride dross or by drossing with caustic soda. Vacuum dezincing of lead was developed as a practical technique in 1946. 

Kroll Bretterton process for bismuth removal 1946 Vacuum dezincing process... 

Fig 12.13 - Schematic of vacuum dezincing equipment. (A) Standard kettle developed by Britannia Refined... 

Davey, T R A and WiUiams, K C, 1956. Continuous vacuum dezincing plant at the BHAS Pty Ltd, Port Pirie, Proceedings Australasian Institute of Mining and Metallurgy, 180 1-11. 

Isbell, W T, 1949. Development of a process for vacuum dezincing of lead. Transactions of the American Institute of Mining, Metallurgical and Petroleum Engineers (AIME), 182 186. 

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