Economic and Performance Comparisons for Aries 100 and Alternative Alkalis

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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
Alkali requirement:
√ per ton H2SO4 1511 dry lb. 2160 dry lb. 1630 dry lb. 1190 dry lb.
√ per ton HCl 2032 dry lb. 2900 dry lb. 2190 dry lb. 1600 dry lb.
√ per ton HNO3 1175 dry lb. 1683 dry lb. 1270 dry lb. 921 dry lb.
Consumption vs. Mg(OH)2 27% more 82% more 37% more
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
Salt in effluent:
√ per ton H2SO4 3510 lb. (insoluble) 2900 lb. 2900 lb. 2460 lb.
√ per ton HCl 3040 lb. 3210 lb. 3210 lb. 2610 lb.
√ per ton HNO3 2603 lb. 2698 lb. 2698 lb. 2349 lb.
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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