Weldon process

The Weldon process is a process developed in 1866 by Walter Weldon for recovering manganese dioxide for re-use in chlorine manufacture. Commercial operations started at the Gamble works in St. Helens in 1869. The process is described in considerable detail in the book, The Alkali Industry, by J.R. Partington,D.Sc.

The common method to manufacture chlorine at the time, was to react manganese dioxide (and related oxides) with hydrochloric acid to give chlorine:

MnO₂ + 4 HCl → MnCl₂ + Cl₂ + 2H₂O

Weldon's contribution was to develop a process to recycle the manganese. The waste manganese(II) chloride solution is treated with lime, steam and oxygen, producing calcium manganite(IV):

2 MnCl₂ + 3 Ca(OH)₂ + O₂ → CaO·2MnO₂ + 3 H₂O + 2 CaCl₂

The resulting calcium manganite can be reacted with HCl as in related processes:

CaO·2MnO₂ + 10 HCl → CaCl₂ + 2 MnCl₂ + 2 Cl₂ + 5 H₂O

The manganese(II) chloride can be recycled, while the calcium chloride is a waste byproduct.

The Weldon process was first replaced by the Deacon process and later by the Chloralkali process.

Further reading

• "The Chlorine industry". Lenntech. Retrieved 11 September 2018.
• Lunge, Georg (1911). "Alkali Manufacture § Preparation of Chlorine" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. pp. 666–66.
• Partington, J.R. (1919). The Alkali Industry. London: Baillière, Tindall & Cox.