Arsenic Contaminated Soil
Immobilization of heavy metals, especially arsenic, may involve both cationic and anionic forms. Arsenic may occur as both cations and anions. Humic mineral concentrates (HMC), including chemically active functional groups, can form complexes to immobilize both cationic and anionic forms.
The efficiency of HMC in binding both cations and anions of heavy metals was demonstrated in lab-scale tests. Then, field tests were carried out on a former industrial disposal site destined for construction of commercial/residential structures. Field test results showed efficiencies of immobilization for zinc of 60%, cadmium of 66%, nickel of 72%, lead of 73%, and strontium of 87%. Arsenic immobilization efficiency was 85%.
The source of arsenic cations was AsCl3 and the source of the anion form was NaAsO2. Both were triple valent ions. Arsenic content in soil samples ranged from 2 mg/kg up to 200 mg/kg. Tests showed that the average efficiency of cationic arsenic immobilization was 90%, for an initial arsenic concentration in soil of 2 mg/kg and 82% for an initial arsenic concentration of 20 mg/kg. Average efficiency of immobilization of anionic arsenic was 85% for an initial arsenic soil concentration of 2 mg/kg and 76% for an initial arsenic concentration of 20 mg/kg. HMC worked well in these trials and is an effective, organic material that is environmentally friendly.