Tribasic Lead Sulfate: Lead Dissolved in Ammonium Acetate with Oxygen, Precipitated

Tribasic lead sulfate is the classic heat stabiliser for rigid PVC. Cox's route (US 4,673,561, 1987) avoids making litharge: metallic lead dissolves in hot ammonium acetate solution under oxygen, ammonia then throws down hydrated lead oxide, and sulphuric acid turns that into tribasic lead sulfate. The ammonia and acetate go round again. The patent got 100 kg from 83.6 kg of lead. The picture: the patent's flow sheet.