Leblanc process

• 1. A Prize Denied

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  The Leblanc process powered 19th-century industry across Europe. Its inventor, Nicolas Leblanc, committed suicide in 1806, denied the prize money that started it all. In 1783, King Louis XVI and the French Academy of Sciences had offered 2400 livres to whoever could make alkali from sea salt.

  Soda ash and potash, together called alkali, were essential to the glass, textile, soap, and paper industries. By the 13th century, deforestation had closed off the traditional European source: potash from burned wood. Britain's only local supply was kelp washed ashore in Scotland and Ireland. Potash had to be imported from North America, Scandinavia, and Russia. Soda ash arrived from Spain, the Canary Islands, and Syria.

  Leblanc was a physician to Louis Philip II, Duke of Orléans. He patented a workable solution in 1791, then built a plant at Saint-Denis that same year. It produced 320 tons of soda per year. The French Revolution seized it before he could collect his prize.

  Saint-Denis was only the beginning. What that process did to factory towns, and what its waste eventually became, are the questions this story follows.

• 2. Two Steps to Soda

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  Carl Wilhelm Scheele, a Swedish chemist, established in 1772 that sodium chloride treated with sulfuric acid would yield sodium sulfate. Leblanc built his process on that foundation. His first step, the Mannheim process, produced sodium sulfate from salt and released hydrogen chloride gas as a byproduct. Early operators simply let that gas escape into the air.

  Leblanc's own contribution was the second step. Salt cake, the name for sodium sulfate, was mixed with crushed limestone and coal. This charge was heated in a reverberatory furnace at around 1000 degrees Celsius. The coal first reduced the sulfate to sodium sulfide. The sodium sulfide then reacted with calcium carbonate to produce sodium carbonate. The dark fused product from the furnace was called black ash.

  Recovering soda ash from black ash required a method called lixiviation. The black ash had to go into water immediately after firing. Delay would let the sulfides oxidize back into sulfate and spoil the batch. Pure water was applied to the most spent ash; the resulting liquor then leached progressively fresher batches. The final liquor was treated with carbon dioxide to precipitate dissolved calcium, then evaporated using waste heat from the furnace, then cooled. Cooling produced nearly pure sodium carbonate decahydrate.

  The coal for the second step had to be low in nitrogen to avoid cyanide formation. The limestone had to be low in magnesia and silica. The weight ratio of salt cake, limestone, and carbon in the furnace charge was 2:2:1. When the reverberatory furnace rotated, workers called it a revolver.

  The hydrogen chloride released in the first step, once treated as an airborne nuisance, would eventually force the British Parliament to act.

• 3. The British Boom

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  The Losh family of iron founders opened the first British Leblanc soda works in 1816 at Walker on the River Tyne. Steep salt tariffs kept British operations modest for the next eight years. The repeal of those tariffs in 1824 changed the scale of the industry entirely.

  The Bonnington Chemical Works was among the earliest producers. James Muspratt built works in Liverpool and Flint. Charles Tennant established operations near Glasgow. Muspratt's Liverpool location gave him a particular advantage: proximity to the Cheshire salt mines, the St Helens coalfields, and the limestone quarries of North Wales and Derbyshire.

  By 1852, British annual soda production had reached 140,000 tons. France that same year produced 45,000 tons. French producers had been first to scale up: by the early 19th century they were making 10,000-15,000 tons annually. Britain, once free of the salt tariff, grew past any comparison.

  By the 1870s, British soda output reached 200,000 tons per year, a figure that exceeded the combined total of every other nation in the world. The communities in the shadow of those factories were already looking for remedies. What they documented would eventually change British law.

• 4. Acid in the Air

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  An 1839 court filing described the experience of living near a soda works in terms that were exact: "the gas from these manufactories is of such a deleterious nature as to blight everything within its influence... the herbage of the fields in their vicinity is scorched, the gardens neither yield fruit nor vegetables; many flourishing trees have lately become rotten naked sticks." That document was part of a genuine lawsuit.

  For every 8 tons of soda ash, the process generated 5.5 tons of hydrogen chloride and 7 tons of calcium sulfide waste. The hydrogen chloride was industrially useless in those early decades and went straight into the atmosphere. The calcium sulfide solid waste, known as galligu, had no commercial value. Factories piled it in heaps and spread it on nearby fields. As it weathered, galligu released hydrogen sulfide, the toxic gas responsible for the smell of rotten eggs.

  In 1863, the British Parliament passed the Alkali Act 1863. It was the first piece of modern air pollution legislation in the world. The act set a ceiling: no more than 5% of the hydrogen chloride produced by alkali works could be released to the atmosphere. Factories responded by passing the gas through towers packed with charcoal, where water flowing in the opposite direction absorbed it. Most then dumped the resulting hydrochloric acid into rivers and coastal waters, killing fish and other aquatic life.

  Workmen cleaning the furnaces sometimes wore cloth gags over their mouths and noses to keep dust and aerosols out of their lungs. The process originally required frequent operator interventions, some involving heavy manual labour. Later mechanization reduced those demands.

  By the 1880s, chemists had found ways to convert hydrogen chloride waste into commercially valuable products. That discovery sustained the Leblanc industry briefly even as a more efficient rival gained ground.

• 5. A Cleaner Rival

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  Ernest Solvay, a Belgian chemist, developed his competing process in 1861. It used ammonia to convert salt and limestone into soda ash. Its only waste product was calcium chloride. It was cheaper to run and far less polluting than the Leblanc method.

  From the late 1870s, Solvay plants on the European continent began undercutting British producers in their home markets. The Brunner Mond Solvay plant, which opened in 1874 at Winnington near Northwich, brought that competition inside Britain itself. Leblanc producers could not match the price of Solvay soda ash.

  Leblanc soda ash became the loss-making part of the operation. The profitable side shifted to byproducts: chlorine, bleaching powder, and related chemicals. The waste that had once been the problem had become the primary reason to keep the factories open.

  When electrolytic methods for producing chlorine arrived, they removed that last advantage. A slow decline followed, eased only by informal agreements between Leblanc and Solvay producers. By 1900-90% of world soda production used the Solvay method.

  On the North American continent, trona, a naturally occurring mineral source of sodium carbonate, was discovered in 1938. That discovery made even the Solvay method unnecessary in North America; the last North American Solvay plant closed in 1986. The last Leblanc soda ash plant in the West had already shut in the early 1920s.

  When Nationalist China evacuated its industry inland during the Second World War, importing and maintaining modern equipment proved too difficult. Engineers temporarily revived the Leblanc process, a method the industrial world had set aside more than two decades earlier.

• 6. Waste as Habitat

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  At Nob End near Bolton, the largest surviving Leblanc process waste site in the United Kingdom now operates as an SSSI and Local Nature Reserve. Only four such sites made it into the new millennium. Three hold formal protection as nature reserves.

  Galligu, the calcium sulfide waste heaped around soda works for decades, does not stay chemically active forever. Over time it weathers into calcium carbonate, creating alkaline soil. In a region where the surrounding geology produces acid soils, such ground is a genuine anomaly. It supports calcicoles: plants that thrive in lime-rich conditions.

  The SSSI designation at Nob End rests largely on its orchid-calcicole flora. Orchids alongside lime-loving species are most unusual in a part of England dominated by acid soils. Yet the Leblanc waste produced exactly the soil chemistry needed to sustain them.

  Acid boiler slag was deposited at Nob End alongside the calcium sulfide waste. That patch of different chemistry now supports a zone dominated by heather. Inside the alkaline reserve sits an acid island shaped by a different class of industrial residue.

  Calluna vulgaris, the species now covering that acid corner, owes its presence to a furnace that stopped burning more than a century ago.