The removal of heavy metals from contaminated soil by a combination of sulfidisation and flotation

• Published in: The Science of the total environment 2002-05, Vol.290 (1), p.69-80
• Main Authors: Vanthuyne, Mathias, Maes, André
• Format: Article
• Language: English
• Subjects: Applied sciences; Availability; Biological Availability; Decontamination. Miscellaneous; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Pollution - prevention & control; Exact sciences and technology; Flotation; Gases; Metal sulfide; Metals, Heavy - analysis; Metals, Heavy - chemistry; Metals, Heavy - isolation & purification; Pollution; Pollution, environment geology; Sequential extraction; Soil and sediments pollution; Soil Pollutants - analysis; Speciation; Sulfides - chemistry; Sulfidisation; Transition metals
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/S0048-9697(01)01064-6

The possibility of removing cadmium, copper, lead and zinc from Belgian loamy soil by a combination of sulfidisation pre-treatment and Denver flotation was investigated. The potentially available — sulfide convertible — metal content of the metal polluted soil was estimated by EDTA (0.1 M, pH 4.65) extraction and BCR sequential extraction. EDTA extraction is better at approximating the metal percentage that is expected to be convertible into a metal sulfide phase, in contrast to the sequential extraction procedure of ‘Int. J. Environ. Anal. Chem. 51 (1993) pp. 135–151’ in which transition metals present as iron oxide co-precipitates are dissolved by hydroxylammoniumchloride in the second extraction step. To compare the surface characteristics of metal sulfides formed by sulfidisation with those of crystalline metal sulfides, two types of synthetic sediments were prepared and extracted with 0.1 M EDTA (pH 4.65) in anoxic conditions. Separate metal sulfides or co-precipitates with iron sulfide were formed by sulfide conditioning. The Denver flotation of both types of synthetic sediments (kerosene as collector at high background electrolyte concentrations) resulted in similar concentrating factors for freshly formed metal sulfides as for fine-grained crystalline metal sulfides. The selective flotation of metal sulfides after sulfide conditioning of a polluted soil, using kerosene or potassium ethyl xanthate as collectors and MIBC as frother, was studied at high background electrolyte concentrations. The sulfidisations were made in ambient air and inside an anoxic glove box. The concentrating factors corrected by the potentially available metal percentage, determined by 0.1 M EDTA extraction, lie between 2 and 3. The selective flotation of these finely dispersed, amorphous, metal sulfides can possibly be improved by optimising the bubble–particle interaction.