Monday, April 28, 2008

Galligu and assorted niceties...

Googling for some thermochemical data on calcium sulfide (CaS) I came across a story that illustrates the kind of progress that's been made in terms of protecting the environment (as well as humans and other life forms that inhabit it) from wasteful activities by industrial scale chemistry. The story's main protagonist is a waste product that was generated in large quantities around the turn of the 19th century, called galligu (a neologism that reflects the black, gooey and stinky nature of that hitherto unknown waste product), in which calcium sulfide features as a prime component. Ironically, my backyard process for producing titanium by means of sulfate boosted thermite reactions generates some calcium sulfide by-product too, albeit in much smaller concentrations and in a dry, fused and much less smelly form (hence my interest in CaS...) Britain has numerous former industrial sites that contain massive deposits of this seriously soil-contaminating waste product (galligu) and we're in a sense still dealing with the legacy of the 'alkali wars'.

The account is that of one of the first industrial chemical processes for the production of a chemical that still today is much sought after: soda ash, aka soda, washing soda, chemically sodium carbonate (Na2CO3). Soluble alkali carbonates had previously for centuries been produced only on a medium scale with more artisan methods, in particular the extraction (leaching with water in designated pots) of potash (potassium carbonate or K2CO3, from which the English word potassium is derived) from wood, plant or kelp ashes (these ashes are quite literally the calcined remains of plant metabolisms).

But demand for soluble alkali (sodium or potassium) carbonates grew exponentially and fueled the need for an industrial conversion of more readily available soluble sodium sources
like sodium chloride (sea salt or kitchen salt) to carbonates.

soda_worksAnd so in 1791, the Frenchman Nicholas Leblanc patented a process that could accomplish just that: converting abundantly available sea salt, combined with equally cheap-as-chips limestone, coal and sulfuric acid with some creative chemistry into that prized commodity: soda.

The Leblanc process must go down in history as one of the most polluting and wasteful industrial processes ever to have been put to massive use: this source here claims totally plausibly that:

In 1862, 1,834,000 tonnes of raw material were used to produce just 280,000 tonnes of saleable product, a ratio of more than 6:1. For every tonne of salt used in the process, three tonnes of coal were burned. It is estimated that one million tonnes of coal were burned annually at the height of Leblanc production. Furthermore, it is known that for every tonne of soda ash produced, two tonnes of waste material (galligu) were generated [...]

It's wastefulness would have been more of an economic problem than anything else, if it hadn't been for the extreme smelliness, indeed toxicity of its waste streams, which in those days were quite unceremoniously dumped, mostly where the factories stood.

galligu_heapsThe galligu itself contains large quantities of calcium sulfide, which due to hydrolysis in the presence of water (galligu is in fact a watery slurry!) generates hydrogen sulfide (H2S), aka rotten eggs or stink bomb gas. Apart from the repulsive odour, perceptible even in trace amounts, H2S is also toxic, more toxic in fact than hydrogen cyanide... In today's terms, Leblanc plants and environs must have been some of the smelliest and toxic places in this green and pleasant land! An 1839 suit against soda works alleged:
"the gas from these manufactories is of such a deleterious nature as to blight everything within its influence, and is alike baneful to health and property. 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. Cattle and poultry droop and pine away. It tarnishes the furniture in our houses, and when we are exposed to it, which is of frequent occurrence, we are afflicted with coughs and pains in the head ... all of which we attribute to the Alkali works."


But there's more. Another, this time gaseous waste product of the Leblanc process is hydrogen chloride (HCl), aka hydrochloric acid, spirit of salt or muriatic acid. Incredibly, back then HCl had no real residual value and Leblanc operators gaily pumped this highly corrosive, pungent smelling and toxic gas through smoke stacks straight into the free atmosphere!

Under pressure from legislators, to this problem a rather hasty and half-hearted solution was found by using primitive gas scrubbers which absorbed the HCl into water, thereby obtaining a dilute solution of hydrochloric acid... which was then simply allowed to flow into nearby water streams with predictably deleterious effects on the water's fauna and flora...

And upstream from the Leblanc process lay an equally polluting process: the production of one of Leblanc's feedstocks: sulfuric acid, back then produced mainly by burning pyrite ores (aka fool's gold, FeS2) that often contained dangerously high levels of heavy metals, among others arsenic, nickel, zinc and chromium...

Not so much later, the Belgian chemist and founder of the Solvay chemical empire, Ernest Solvay, developed a sulfurless means of soda production (the Solvay process) which was overall almost squeaky clean and fairly quickly replaced all Leblanc capacity.

Those who today still believe that G-d's green Earth has an infinite capacity for healing and that it's therefore OK to pollute to one's heart's content should accepts that careless and wasteful (albeit also highly useful) industrial activity can lay waste to large areas of the human environment for decades...

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