Editing Leblanc process (section)

== Chemistry ==
[[File:Leblanc process reaction scheme.svg|thumb|250px|Reaction scheme of the Leblanc process (green = reactants, black = intermediates, red = products)]]
In the first step, sodium chloride is treated with [[sulfuric acid]] in the [[Mannheim process]].  This reaction produces [[sodium sulfate]] (called the ''salt cake'') and [[hydrogen chloride]]:
: 2 NaCl + H<sub>2</sub>SO<sub>4</sub> → Na<sub>2</sub>SO<sub>4</sub> + 2 HCl

This [[chemical reaction]] had been discovered in 1772 by the [[Sweden|Swedish]] chemist [[Carl Wilhelm Scheele]].  Leblanc's contribution was the second step, in which a mixture of the salt cake and crushed [[limestone]] ([[calcium carbonate]]) was reduced by heating with [[coal]].<ref>{{cite encyclopedia|author=Christian Thieme|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|location=Weinheim|year=2000|doi=10.1002/14356007.a24_299|isbn = 978-3527306732|chapter = Sodium Carbonates}}</ref>  This conversion entails two parts. First is the [[carbothermic reaction]] whereby the coal, a source of [[carbon]], [[Redox|reduces]] the [[sulfate]] to [[sulfide]]:
: Na<sub>2</sub>SO<sub>4</sub> + 2&nbsp; C → Na<sub>2</sub>S + 2&nbsp;CO<sub>2</sub>

In the second stage, is the reaction to produce [[sodium carbonate]] and [[calcium sulfide]]. This mixture is called ''black ash''.{{Citation needed|date=January 2021}}

: Na<sub>2</sub>S + CaCO<sub>3</sub> → Na<sub>2</sub>CO<sub>3</sub> + CaS
The soda ash is extracted from the black ash with water.  Evaporation of this extract yields solid sodium carbonate.  This extraction process was termed lixiviation.{{Citation needed|date=January 2021}}

In response to the [[Alkali Act]], the noxious calcium sulfide was converted into calcium carbonate:
:{{chem2|CaS(s) + CO2(g) + H2O(l) -> CaCO3(s) + H2S(g)}}

The [[hydrogen sulfide]] can be used as a sulfur source for the [[lead chamber process]] to produce the [[sulfuric acid]] used in the first step of the Leblanc process.

Likewise, by 1874 the [[Deacon process]] was invented, oxidizing the hydrochloric acid over a copper catalyst:
:{{chem2|4 HCl(g) + O2(g) -> H2O(g) + Cl2(g)}}

The chlorine would be sold for bleach in paper and textile manufacturing. Eventually, the chlorine sales became the purpose of the Leblanc process. The inexpensive chlorine was a contributor to the development of the [[chloralkali process]].{{Citation needed|date=October 2024}}