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white powdery substance 1

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EnviroChemGirl

EnviroChemGirl

Civil/Environmental
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I found a light white powdery substance with a pH of 13 on a Phase I ESA site. The powder does not react with HCl. Any ideas as to what the powdery substance is? The site used to manufacture acetylene in the 70's.
 
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It is probably calcium sulfate.

One of the waste products from acetylene is a lime sludge. The lime sludge is usually neutralized with waste acid to form calcium sulfate.

The principal raw materials for acetylene manufacture are calcium carbonate (limestone) and coal. The calcium carbonate is first converted into calcium oxide and the coal into coke, then the two are reacted with each other to form calcium carbide and carbon monoxide:

CaO + 3C ? CaC2 + CO

Calcium carbide (or calcium acetylide) and water are then reacted by any of several methods to produce acetylene and calcium hydroxide.

CaC2 + 2H2O ? Ca(OH)2 (waste) + C2H2 (acetylene)

Ca(OH)2 + H2SO4 ? CaSO4 + H2O



 
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It is probably calcium sulfate.

One of the waste products from acetylene is a lime sludge. The lime sludge is usually neutralized with waste acid to form calcium sulfate.

The principal raw materials for acetylene manufacture are calcium carbonate (limestone) and coal. The calcium carbonate is first converted into calcium oxide and the coal into coke, then the two are reacted with each other to form calcium carbide and carbon monoxide:

CaO + 3C -> CaC2 + CO

Calcium carbide (or calcium acetylide) and water are then reacted by any of several methods to produce acetylene and calcium hydroxide.

CaC2 + 2H2O -> Ca(OH)2 (waste lime) + C2H2 (acetylene)

Ca(OH)2 + H2SO4 -> CaSO4 + H2O


 
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After reading your post, there remains a little mystery regarding the pH. If the material is a lime sludge, it definitely will have a pH of 13. The lime sludge should also react with the HCL. Perhaps the waste needs to be hydrated with water first. If the lime sludge has been neutralized with acid, the material will be calcium sulfate with a neutral pH.

Perhaps, the pH value is not from a representative sample. Or maybe the material is a mixture of calcium sulfate and lime.

Some time ago I worked at a plant where the byproduct lime waste was given to a neighboring facility where it was used to neutralize excess waste acid from refrigerant manufacturing.
 
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