Chalk Ballast
Plants using waste materials are usually geographically disconnected from their raw material’s ultimate source. The most significant category of waste usage is the large number of small plants that grew up using chalk ballast. Coal from the northeast of England has been the preferred fuel in London virtually since its foundation two thousand years ago. Since London produced no low-value cargoes for the coal ships on their return journeys, it became normal practice to ballast them using the cheapest available bulk material – chalk quarried from the banks of the Thames estuary. The result was the uninterrupted series of quarries along the Thames in the Grays and Northfleet areas, and vast stockpiles of chalk surrounding the dock areas in northeast ports such as Hull, Tees-side, Hartlepool and Tyneside. The latter were massive: the old Ordnance Survey maps label them “ballast hill”. Several were high enough and permanent enough to have trigonometric points on their summits. The small cement plants that grew up on the river banks literally quarried them. They were not an entirely reliable material source, since various other ballast materials such as gravel or china clay tailings were indiscriminately mixed in with the chalk. The North-east became the only area outside the Thames/Medway district making an appreciable amount of Portland cement. A contemporary description of the district is given here. As the chalk stockpiles depleted, and when iron coal-ships with pumpable water ballast were developed, these plants ended up shipping chalk from the Thames as commercial cargoes, until they gave up the ghost due to the resulting high production cost. In many cases, the shut-down of coastal trade during WWI was decisive. This reliance on a distant chalk-source occurred even when quite good limestones were available locally – a result of the mystical cement-making qualities originally attributed to Thames chalk.
Despite the superabundance of chalk in Britain, I found an example of imported chalk being used, on the same "return-load" basis. The cement plants at Aalborg, Denmark, routinely obtained their coal supply from Tyneside, and a Hartlepool firm, E. A. Casper & Co. (originating from Aalborg) shipped coal there and ballasted with Rørdal chalk for the return trip. Some plants in the Hamburg area may have done the same.
The plant names on this map are now clickable unless re-sized by device.
Precipitated Calcium Carbonate
Some other industries produced calcium carbonate as a waste, notably the alkali industry on the Mersey, Tyne and Tees. Although the chemical industries needed calcium carbonate as a raw material, precipitated calcium carbonate, obtained as a cake, mud or sludge, could not be re-cycled in old-fashioned lime kilns before the advent of the rotary lime kiln, and vast quantities were discarded, usually by literally flushing them “down the drain”. On the other hand, a wet process cement plant could handle them without much trouble.
In the Leblanc Process for making sodium carbonate, calcium sulfide is produced as waste:
2NaCl + H2SO4 → Na2SO4 + 2HCl
Na2SO4 + CaCO3 + 2C → Na2CO3 + CaS + 2CO2
Under pressure from the Alkali Inspectorate, the Chance Process was developed to consume the huge noxious mountains of calcium sulfide that had built up in the nineteenth century:
CaCO3 → CaO + CO2
CaS + CO2 + H2O → CaCO3 + H2S
2H2S + O2 → 2S + 2H2O (using a Fe2O3 catalyst)
The calcium carbonate produced, being too fine to re-burn as lime, was used as part of a cement rawmix. The only plant dedicated to using this process appears to have been that attached to Chance’s own alkali plant at Oldbury, although Ditton and Jarrow used it among a cocktail of other wastes.
The process of conversion of sodium carbonate to sodium hydroxide also produced calcium carbonate as a fine filter cake that was otherwise dumped:
CaCO3 → CaO + CO2
CaO + H2O → Ca(OH)2
Na2CO3 + Ca(OH)2 → 2NaOH + CaCO3
Many plants used this at least for part of their lives, those after 1895 being Crosfield's, Ditton, Gateshead and Jarrow. This “causticisation” process was also used in soda recovery in the paper industry:
Lignin + NaOH → Sodium Lignate
Sodium Lignate → Na2CO3 (by pyrolysis)
Na2CO3 + Ca(OH)2 → 2NaOH + CaCO3
At least one plant (South Hylton) used the carbonate sludge as a raw material. This source dried up with the conversion of paper making to the sulfite process.
At Billingham, the adjacent synthetic ammonia plant used the Haber process to make ammonia. Ammonia was reacted with hydrogen plant CO2 to form ammonium carbonate, and this was reacted with finely-ground anhydrite to form ammonium sulfate and calcium carbonate as “sulfate plant mud” that was previously dumped in the North Sea:
2NH3 + H2O + CO2 → (NH4)2CO3
(NH4)2CO3 + CaSO4 → (NH4)2SO4 + CaCO3
The conventional cement plant started using this in 1924: it became its sole carbonate source in 1928. The mud was also used by Warren, 1924-1929. This process is discussed in detail in the Billingham page.
At least one sugar refinery had an attached cement plant: lime was used to carry down impurities in sugar liquor:
CaCO3 → CaO + CO2
CaO + H2O → Ca(OH)2
Sugar + Ca(OH)2 → Calcium saccharate
Calcium saccharate + CO2 → Sugar + CaCO3
Until rotary lime kilns were developed, the resulting calcium carbonate was too fine to re-burn.
Plants using carbonate waste began to proliferate after 1890, the imperatives driving this being typified by Crosfield's, who had been prosecuted for dumping their waste in the Mersey. Nonetheless, this source was of limited duration, because the chief sources in the alkali industry were at the same time moving towards more efficient waste-free processes – notably the electrolytic processes for making sodium hydroxide. Carbonate waste was further eliminated by the development of rotary lime kilns which could easily re-burn the otherwise intractable carbonate sludges. The one long-standing plant at Billingham remained – by cement industry standards – extremely inefficient. As a minor excrescence of ICI’s business, there was little pressure to drive down costs as long as favourable pricing and ignored incidental expenses kept the balance sheet more or less in the black.
Blast Furnace Slag
Around the beginning of the twentieth century, the lack of locally produced cement in Scotland prompted a number of Scottish iron works to consider re-burning their blast-furnace slag with extra limestone to make a clinker, subsequently inter-ground with more slag to make a pbfc. “Activated slag” cement had been made for some time by inter-grinding water-granulated slag with calcium and/or sodium hydroxides, but this was too slow a cement even by the standards of the day. In the USA, rejection of this product led to the making of portland clinker from slag and limestone in 1900 , and accounted for 13% of US output by 1912, peaking at over two million tonnes per year. The largest plant using the process, at Buffington IN, had a capacity at that time of 4800 t/day from 40 kilns, making it the largest plant in the US, and therefore the world. The use of slag in Portland rawmixes had been examined in the UK, but rejected because of the weakness and friability of the briquetted rawmix, which prevented its use in static kilns. The process had to wait for the introduction of the rotary kiln. In the UK, the process began to be used when it was already in decline in the US, and it never developed outside Scotland, where conventional cement raw materials were hard to find. Only low-magnesia slag could be used, and the 20th century trend towards higher magnesia in slags made the process progressively less viable. In Scotland, used at Coltness and Wishaw, it provided the only indigenous cement between the closure of Cousland in 1923 and the opening of Dunbar in 1963.
The Scottish slag-burning plants all started out by installing the Colloseus patent process for making ground activated slag. Substantial capital was invested before, as happened in the USA, the complete rejection of the product by the market led them to investigate making a Portland product. Others, notably in the North-east, had examined the possibility of making the Colloseus product – Consett iron works was to supply the slag – but the idea was never carried through (although a great deal of cement with slag in it was undoubtedly sold surreptitiously). This left only the Scottish plants. All had lost their on-site blast furnaces by 1930, and continued by quarrying the massive slag-"bings" that had been built in the previous century, and by buying in slag from the diminishing number of plants remaining in Scotland. The availability of low-Mg slag in particular diminished after WWII, and the slight raison d’être of the plants was eliminated with the prospect of a large conventional plant in the form of Dunbar. The rotary kilns exclusively used were all dry process, the early difficulties with this being less in evidence due to the forgiving nature of the slag rawmix. In principle, high efficiency should have been possible, but the operations were far too small to allow the necessary investment to bring this about, and fuel consumptions remained mediocre.
The Anhydrite Process
Included for convenience here are the plants making sulfuric acid by the “Anhydrite Process” , in which cement clinker itself was a by-product. This is covered in a separate article.