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Comparison basis | Hydrated lime calcium hydroxide | Soda ash sodium carbonate | Caustic soda sodium hydroxide | Aries 100 magnesium hydroxide | |||||||||||||||||||||||||
Product form | powder – Ca(OH)2 available as slurry to 35% solids | powder – Na2CO3 available as 15% solution | 50% solution – NaOH | 59% solids slurry – Mg(OH)2 | |||||||||||||||||||||||||
Raw material cost (ton per ton basis) | least expensive | about half the cost of magnesium hydroxide | fluctuates widely with supply; often more expensive than Mg(OH)2 | generally competitive with caustic soda; pricing consistent | |||||||||||||||||||||||||
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Capital investment | high due to solids handling and slaking; also regular maintenance of system due to calcium deposits | least expensive; costs associated with solubilizing the powder, controlling foaming, and metals carryover | cost associated with safety considerations; no agitated tank required; freeze protection needed for 50% caustic | agitated storage tank required | |||||||||||||||||||||||||
Residence time | moderately fast acting to complete neutralization | moderately fast acting to complete neutralization | extremely fast acting to complete neutralization | moderately fast acting to 95% of neutralization; more controllable process | |||||||||||||||||||||||||
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Maximum pH in overtreatment | 12 | >11 | 14 | 9 | |||||||||||||||||||||||||
Sludge produced | heavy sludge containing calcium sulfate (gypsum) if neutralizing sulfuric acid | high volume, gel-like with heavy metals | high volume, gel-like with heavy metals | dense, low volume with heavy metals; easier to dewater | |||||||||||||||||||||||||
Safety | moderately hazardous material | moderately hazardous material | hazardous material requiring rigorous safety procedures | nonhazardous material | |||||||||||||||||||||||||
Environmental | can overshoot desired pH | sodium ion discharge | sodium ion discharge can easily overshoot desired pH | buffers at pH 9 |
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