Patent GB-239257-A (GB)
Title: Conversion of lead sulphate into lead carbonate
IPC: C01G21/14
Filed: 1924-05-05
Abstract: Ammonium sulphate is produced during the conversion of lead sulphate into lead carbonate.  The lead sulphate is agitated with excess of ammonia, and carbon dioxide is introduced.  The treatment with carbon dioxide may be effected simultaneously with the ammonia treatment, or the carbon dioxide may be wholly or in part dissolved in the ammonia, or the carbon dioxide treatment may be effected after the lead hydroxide has been formed and while it is suspended in its mother-liquor, or after it has been separated from its mother-liquor. The carbonation may be effected first at a comparatively low temperature such as 30 DEG  C., and then at a higher temperature, say 40-50 DEG  C. or higher, 70 DEG  C. being mentioned.  The reaction may be effected in counter-current, and the ammonium sulphate liquor may be so strong as to be ready for crystallization.  Ammonia may be added during the carbonation to replace that carried away by the gases.  When the reaction is finished, the mother-liquor is divided, one part, called the nucleus liquor, being made up by the addition of ammonia, water, and lead sulphate for another operation, while the other part, called the residual liquor, is treated to recover the constituents, for instance by distilling with lime.  The process may be combined with processes in which lead is extracted from ores as sulphate or chloride.  In the latter case the chloride is converted into sulphate as described in Specification 239,559, [Class 1 (iii), Oxides &c., Metallic].ALSO:Lead sulphate is converted into carbonate by agitation with ammonia solution in excess so as to produce the hydrate and passing carbon dioxide, or gases containing it through the suspension until the conversion is effected.  The treatment with carbon dioxide may be effected simultaneously with the ammonia treatment, or the carbon dioxide may be wholly or in part dissolved in the ammonia, or the carbon dioxide treatment may be effected after the lead hydroxide has been formed and while it is suspended in its mother-liquor or after it has been separated from its mother-liquor. The carbonation may be effected first at a comparatively low temperature such as 30 DEG  C. and then at a higher temperature, say 40-50 DEG  C. or higher, 70 DEG  C. being mentioned. The reaction may be effected in counter-current, the lead sulphate being first treated with a liquid in which part of the ammonia has already been converted into ammonium sulphate and then with fresh liquor, and the ammonium sulphate liquor may be so strong as to be ready for crystallization. Ammonia may be added during the carbonation to replace that carried away by the gases.  When the reaction is finished and the lead carbonate is separated, the mother-liquor is divided, one part, called the nucleus liquor, being made up by the addition of ammonia, water, and lead sulphate for another operation, while the other part, called the residual liquor is treated to recover the constituents, for instance by distilling with lime.  The process may be combined with processes in which lead is extracted from its ores &c. as sulphate or chloride.  In the latter case the chloride is converted into sulphate for instance by treatment with zinc sulphate as described in Specification 239,559.