GB500961A - Improvements in the manufacture of white lead - Google Patents

Abstract

500,961. White lead. ROBINSON BROS., Ltd., PARKES, D. W., and EVANS, R. B. Aug. 17, 1937, No. 22602. Drawings to Specification. [Class 1 (iii)] White lead is produced by passing carbon dioxide into basic lead acetate solution under such conditions that as the reaction proceeds, the lead carbonate content of the precipitate falls to a recognizable minimum and then increases, the introduction of carbon dioxide being terminated at a point past this minimum, but before the lead carbonate content exceeds 80 per cent. The precipitate is maintained in suspension throughout the reaction by mechanical stirrers or merely by the agitation caused by the introduction of gas containing a relatively low proportion of carbon dioxide. Elevated temperatures between 18 and 60‹ C., and increased pressures, e.g. 5 to 30 lb. sq. in. using pure carbon dioxide, facilitate the production of an easily recognizable point of minimum carbonate content, a temperature of 20-26‹ C. and pressure of 10-11 lb. sq. in. being especially suitable. Employing a gas containing 13-18 per cent carbon dioxide, e.g. a gas obtained by burning coke (15-17 per cent carbon dioxide), a pressure of 80 lb. sq. in. may be used. The course of the reaction may be followed by determination of the sp. gr. of the mother liquor, which, when the precipitate is maintained in suspension, falls continuously to a point corresponding to the minimum carbonate content, and thereafter remains constant. The carbon dioxide may be introduced through perforated lead coils, and the carbonator may be water jacketed. The precipitate, which should be removed from the liquor as soon as carbonation stops, is washed and dried, preferably at 50-70‹ C. Several examples are given, the basic lead acetate solution being obtained by treating oxidized lead with acetic acid, or with the mother liquor of a previous operation.