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The Making of Alkali in Widnes
Stages in the Lablanc Process
by Bob Roach
First Stage - Manufacture of sulphuric acid.
This needed a source of sulphur, the one ingredient that wasn’t available nearby. A major source of this was iron pyrites (a chemical made up of iron and sulphur). Whatever the source, sulphur was an expensive ingredient.
As sulphuric acid was difficult to transport due to its highly corrosive properties, it was usually manufactured at Leblanc factories for immediate use. This was what Hutchinson did.
Heating pyrites in a furnace released the sulphur which was used to produce sulphuric acid. The two arched brick buildings on Spike Island that are featured in the Urban Heritage walk were probably built to protect already fairly derelict remains of pyrites furnaces. With iron pyrites being a mined rather than a manufactured resource, it tends to contain a range of other chemicals such as copper, arsenic and small amounts of silver. As a result of the quantity of pyrites being burned in Widnes by several other factories that were set up following Hutchinson’s lead, several copper recovery businesses were set up locally. NAMES
A major source of pollution of the Leblanc process was that this expensive material, so essential for getting things underway, finished up as waste, and waste that remains unpleasantly smelly and noxious on a long term basis because of the sulphur. There was a vast amount of it dumped on large areas of ground around Widnes.
Second Stage - Produce Salt Cake
Salt cake Manufacture. The salt being charged into the salt cake pot, 1880's.
Sulphuric acid and salt (brought from mid-Cheshire) were heated to a temperature well above that of boiling water and the mixture was stirred. Initially, this was done by hand using very long and heavy metal poles - there are several in the heritage area /museum at Catalyst. Later, a mechanical means of stirring was introduced.
This produced a substance called saltcake, the desired product at this stage, and also hydrogen chloride gas, then known as muriatic acid.
Initially, nothing was done to make use of the hydrogen chloride, and it was released into the atmosphere, killing any nearby vegetation. Although this gas could readily be absorbed in water to remove it from the atmosphere, it was only when threatened with Government action that Leblanc factory owners did this.
Even then, making the local water courses acidic wasn’t ideal because it killed off any life that had been there.
It would be some years before ingenious industrialists found ways to convert this hydrogen chloride to chlorine, a chemical that was useful. Some of the pioneering work to do this was done by local industrialist Henry Deacon and his chemist Ferdinand Hurter.
Third Stage - Produce Black Ash
The Mechanisation of an old technology- a revolving black ash furnace at Widnes Alkali Works, early 1880's
Crushed limestone and powdered coal were added to the saltcake and heated in a revolving furnace at a high temperature to produce Black Ash. This was a mix of Soda Ash (the required product) and other chemicals. This was run off from the furnace into metal trucks where it was then allowed to cool to a solid in the trucks.
Fourth Stage - Extract Soda Ash from the Black Ash
The Sledgehammer gang
Having solidified on cooling, the blocks of Black Ash were tipped out of the metal trucks and broken up by men wielding sledgehammers. Being the only soluble component, the soda ash was separated from the other material by dissolving it in hot water. Once so separated, the excess water was boiled off, crystalizing the soda ash in the process.
Waste from Leblanc Factories
There was at least 2 tons of noxious (noxious because of the sulphur) for every ton of soda ash produced. Over the decades vast amounts of this waste were dumped in many locations - such sites remain toxic now. Many local people over the age of 70 will recall the area known as ‘Ditton Alps’ that was more or less where Dundalk Rd is now in Widnes. Many more will recall the attempt to make Ditton Alps' a golf course in that area - initially, it was successful, but the pollution eventually broke through the covering layer. Hopes of being able to deal with the pollution and re-open the golf course were abandoned about 10 years ago.
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