1. © Oxford University Press 2011 IC3.6.4 The Leblanc process The Leblanc process

2. © Oxford University Press 2011 IC3.6.4 The Leblanc process Nicolas Leblanc. The French chemist who invented a process for making alkali from salt and limestone. Using this process, an alkali industry grew up in the 1800s in Widnes, Northwest England.

3. © Oxford University Press 2011 IC3.6.4 The Leblanc process Pollution over Widnes in 1895. Leblanc’s process produced lots of waste. In 1862, nearly 2 million tonnes of raw materials were used to produce just a quarter of a million tonnes of product. The rest was waste. For every tonne of salt used, three tonnes of coal were burned.

4. © Oxford University Press 2011 IC3.6.4 The Leblanc process The Leblanc process salt (sodium chloride) hydrogen chloride gas coal (carbon) limestone (calcium carbonate) solid waste (calcium sulfide) alkali - soda ash (sodium carbonate) sulfuric acid from pyrites (iron sulfide) salt cake (sodium sulfide)

5. © Oxford University Press 2011 IC3.6.4 The Leblanc process A polluting process 1 tonne of alkali 0.75 tonnes 2 tonnes hydrogen chloride solid waste

6. © Oxford University Press 2011 IC3.6.4 The Leblanc process By 1891, over 200 hectares around Widnes were buried under an average of 4 metres of solid waste from the alkali industry. Hydrogen chloride, from the factory chimneys, dissolved in rainwater to produce acid rain. The acid rain damaged buildings and wildlife. It also reacted with the solid waste to release foul-smelling hydrogen sulfide gas.

7. © Oxford University Press 2011 IC3.6.4 The Leblanc process The 1863 Alkali Act limited emissions of hydrogen chloride gas. William Gossage invented a way of removing hydrogen chloride from the chimney gases produced by the alkali factories. The process produced hydrochloric acid which was then put down the drain! Cleaning up the process hydrogen chloride gas from furnaces water trickling down hydrochloric acid tower packed with coke

8. © Oxford University Press 2011 IC3.6.4 The Leblanc process Cleaning up the process In 1874, Henry Deacon invented a way to use the hydrogen chloride gas to make chlorine. In the process, hydrogen chloride gas is oxidised to produce chlorine, a useful product. oxygen hydrogen chlorine

9. © Oxford University Press 2011 IC3.6.4 The Leblanc process Cleaning up the process The problems of the Leblanc process were solved by developing new methods for manufacturing alkalis. Widnes1895 Widnes 2010