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Weldon process
Introduction
The Weldon process is a process developed in 1870 by Walter Weldon for recovering manganese dioxide for re-use in chlorine manufacture.
After reacting hydrochloric acid with manganese dioxide (and related oxides), the waste manganese(II) chloride solution is treated with lime, steam and oxygen, producing calcium manganite (IV):
2MnCl2 + 3Ca(OH)2 + O2 → CaO·2MnO2 + 3H2O + 2CaCl2
The resulting calcium manganite can be reacted with HCl as in related processes:
CaO·2MnO2 + 10HCl → CaCl2 + 2MnCl2 + 2Cl2 + 5H2O
The MnCl2 can be recycled, while the CaCl2 is a waste byproduct.