GB477230A - Manufacture of sodium hydroxide - Google Patents

Abstract

Sodium oxalate is precipitated by reacting a suitable metal oxalate and a soluble sodium salt, e.g. sodium chloride or nitrate, the acid radicle of which forms a soluble calcium salt, in the presence of water and a volatile alkali, e.g. ammonia or trimethylamine. The metal oxalate must be soluble in the presence of the alkali and the metal must give a soluble compound with the acid radicle of the sodium salt. Suitable oxalates are those of Cu, Zn, Ni, Ag, Co, and Cd.ALSO:Sodium hydroxide is prepared by reacting, in the presence of water and a volatile alkali, a suitable metal oxalate and a soluble sodium salt, e.g. the chloride or nitrate, the acid radicle of which forms a soluble calcium salt to precipitate sodium oxalate, causticizing this with lime to give sodium hydroxide and a precipitate of calcium oxalate, and reacting this precipitate with the mother liquor from the first stage, after removing at least part of the volatile alkali and adding acid to dissolve soluble constituents of the resulting precipitate, to precipitate the original metal oxalate. This oxalate must be soluble in the presence of the volatile alkali but less soluble than calcium oxalate, and the metal must yield soluble salts capable of reacting with calcium oxalate and of separation from the alkali to permit recovery thereof, and the compound of the metal and the acid radicle of the sodium salt must be soluble. Suitable metal oxalates include those of Cu, Zn, Ni, Ag, Co and Cd. In modifications, the precipitated calcium oxalate is added to the mother liquor prior to removal of volatile alkali or the alkali is removed, the resulting precipitate separated, treated with acid, and reacted with the calcium oxalate. Ammonia is the preferred alkali but other volatile alkalis, e.g. trimethylamine, may be used. The causticizing with lime is preferably carried out in two stages. Removal of volatile alkali may be effected by distillation in steam.