NEUTRALISATION OF ARSENIC RICH WATER WITH LIMESTONE

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NEUTRALISATION OF ARSENIC RICH WATER WITH
LIMESTONE

• By
• Njabulo Mbhele

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Background

• Arsenic rich water is generated during the
  Bio-Oxidation (BIOX) leaching process
• BIOX process uses bacteria to decompose and
  oxidise sulphides containing gold.
• Currently lime is used to neutralize the acid
  water

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Objectives

• Identify the most suitable limestone source for
  neutralization of arsenic water.
• Compare lime and limestone sludge to meet
  Toxicity Characteristic Leaching Procedure (TCLP)
  specs.
• Provide design criteria for neutralization of
  acid water with powder CaCO3

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Chemical composition of feed water
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Sources of limestones

• Sappi Enstra
• Ngodwana
• Syferfontein
• TSB
• Highveld limestone

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Process flow diagram
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Results
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Comparison between cost of lime and limestone
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Conclusions

• Limestone (Ngodwana) can be used effectively to
  replace lime for neutralization process.
• The cost of limestone will amount to 46 less
  than that of lime.
• Acidity can be removed from 33.6 to 0.06 g/l as
  CaCO3 and arsenic to less than 0.34 mg/l.
• There is no significant difference in the TCLP
  sludge values when treated with lime or limestone.