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On the Engis site, PRAYON begins sodium hydrosulphite production by the "zinc process", with an initial capacity of 400 t a year. Many improvements in both the process and facility are quickly made.

Hydrosulphite production then increases steadily as the years go by.


An ambitious modernisation programme is launched to raise the facility’s capacity to 13 000 t a year.


PRAYON begins marketing sodium hydrosulphite in solution.

In parallel to this, the company is increasingly keen to get the most value from zinc hydroxide, which is a by-product of hydrosulphite production. Various contacts are then made, notably with the French company SILAR.


SILOX (Société Industrielle Liégeoise des Oxydes) is created on 22 December 1983 as a 50/50 joint venture between SILAR and the chemicals concern PRAYON-RUPEL to produce zinc oxides, mainly for the rubber industry, at Engis.

SILOX’s business grows steadily, thanks in particular to the quality of its active ZnO. Its output of oxides rises gradually.


The business unit encompassing the company’s liquid SO2 and sodium hydrosulphite production plants are transferred from PRAYON to SILOX.

SILOX then becomes an integrated producer of sulphurous anhydride(SO2), a range of sodium hydrosulphite-based reducing agents, and a range of zinc oxides.


Launch of a major plant modernisation and capacity upgrade plan.

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