The technologies available for metals insolubilisation are:

• Precipitation as hydroxide. Lime or caustic are added, usually to the pH of minimum solubility. This process has limitations in cases where multiple metals are present with a pH range of minimum solubility.

• Precipitation as carbonate.

• Precipitation as sulphide. This process has the advantage of having a wide range of minimum solubility. The disadvantage is that a poorer thickening sludge is generated and sulphide presents a potential odour and health hazard.
  Sulphide precipitation may be accomplished with inorganic sulphide as  sodium sulphide or several sulphide rich organic compounds.

Injections into the Soil of Sodium Sulphide, ready to use solutions are easier and safer to implement.