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 | |||||||||||||||||||||||||
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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 | |||||||||||||||||||||||||
| Hydrated Lime calcium hydroxide | |
|---|---|
| Product form | powder – Ca(OH)2 available as slurry to 35% solids |
| Raw material cost | least expensive |
| Alkali requirement per ton H₂SO₄ | 1511 dry lb. |
| Alkali requirement per ton HCl | 2032 dry lb. |
| Alkali requirement per ton HNO₃ | 1175 dry lb. |
| Consumption vs Mg(OH)₂ | 27% more |
| Capital investment | high due to solids handling and slaking; also regular maintenance of system due to calcium deposits |
| Residence time | moderately fast acting to complete neutralization |
| Salt per ton H₂SO₄ | 3510 lb. (insoluble) |
| Salt per ton HCl | 3040 lb. |
| Salt per ton HNO₃ | 2603 lb. |
| Max pH in overtreatment | 12 |
| Sludge produced | heavy sludge containing calcium sulfate (gypsum) if neutralizing sulfuric acid |
| Safety | moderately hazardous material |
| Environmental | can overshoot desired pH |
| Soda Ash sodium carbonate | |
|---|---|
| Product form | powder – Na2CO3 available as 15% solution |
| Raw material cost | about half the cost of magnesium hydroxide |
| Alkali req. per ton H₂SO₄ | 2160 dry lb. |
| Alkali req. per ton HCl | 2900 dry lb. |
| Alkali req. per ton HNO₃ | 1683 dry lb. |
| Consumption vs. Mg(OH)₂ | 82% more |
| Capital investment | least expensive; costs associated with solubilizing the powder, controlling foaming, and metals carryover |
| Residence time | moderately fast acting to complete neutralization |
| Salt per ton H₂SO₄ | 2900 lb. |
| Salt per ton HCl | 3210 lb. |
| Salt per ton HNO₃ | 2698 lb. |
| Maximum pH | >11 |
| Sludge produced | high volume, gel-like with heavy metals |
| Safety | moderately hazardous material |
| Environmental | sodium ion discharge |
| Caustic Soda sodium hydroxide | |
|---|---|
| Product form | 50% solution – NaOH |
| Raw material cost | fluctuates widely with supply; often more expensive than Mg(OH)2 |
| Alkali req. per ton H₂SO₄ | 1630 dry lb. |
| Alkali req. per ton HCl | 2190 dry lb. |
| Alkali req. per ton HNO₃ | 1270 dry lb. |
| Consumption vs. Mg(OH)₂ | 37% more |
| Capital investment | cost associated with safety considerations; no agitated tank required; freeze protection needed for 50% caustic |
| Residence time | extremely fast acting to complete neutralization |
| Salt per ton H₂SO₄ | 2900 lb. |
| Salt per ton HCl | 3210 lb. |
| Salt per ton HNO₃ | 2698 lb. |
| Maximum pH | 14 |
| Sludge produced | high volume, gel-like with heavy metals |
| Safety | hazardous material requiring rigorous safety procedures |
| Environmental | sodium ion discharge can easily overshoot desired pH |
| Aries 100 magnesium hydroxide | |
|---|---|
| Product form | 59% solids slurry – Mg(OH)2 |
| Raw material cost | generally competitive with caustic soda; pricing consistent |
| Alkali req. per ton H₂SO₄ | 1190 dry lb. |
| Alkali req. per ton HCl | 1600 dry lb. |
| Alkali req. per ton HNO₃ | 921 dry lb. |
| Consumption vs. Mg(OH)₂ | |
| Capital investment | agitated storage tank required |
| Residence time | moderately fast acting to 95% of neutralization; more controllable process |
| Salt per ton H₂SO₄ | 2460 lb. |
| Salt per ton HCl | 2610 lb. |
| Salt per ton HNO₃ | 2349 lb. |
| Maximum pH | 9 |
| Sludge produced | dense, low volume with heavy metals; easier to dewater |
| Safety | nonhazardous material |
| Environmental | buffers at pH 9 |
