Many industries are aware of the opportunities to recover valuable resources from process and bleed streams. This combines creating revenues from waste streams with environmental sustainability. Even low concentrations of dissolved base metals can be economically recovered.
There are numerous streams with relatively small concentrations of metals (10 ~ 1000 mg/l) of base metals like copper, zinc or nickel. Removal of these metals typically means bulk precipitation as hydroxide in gypsum slurry during lime precipitation. The metal value by itself is attractive but recovery of the metals from this mix is seldom economically attractive.
Metal sulphide precipitation is superior to metal hydroxide precipitation because it has the many advantages:
- High reactivity of sulphides with heavy metal ions and very low solubility of the resulting metal sulphides over a broad pH range resulting in lower effluent concentrations
- Metal sulphide sludges are denser and have better thickening and dewatering characteristics than metal hydroxide sludges, which facilitates further processing
- An easily marketable, compact product is formed
- High degree of selective precipitation is easily accomplished
- Relatively insensitive to the presence of complexes and most chelating agents
- Chromates and dichromates without separate reduction of the chromium
Previous objections against the use of sulphide, i.e. that it is dangerous and corrosive, do not hold anymore because of the application of adequate safety measures and the use of modern corrosion-resistant construction materials (plastics). Recovery of low concentrations of metals with sulphide would be the method of choice, if the high cost of transporting, storing or producing sulphide on-site (as NaSH or H2S) would not have hampered its widespread application in the metal and mining industry.
Paques’ THIOTEQ™ and SULFATEQ™ technologies offer the alternative for economically attractive metal recovery. These processes produce sulphide from elemental sulphur or sulphate under ambient conditions. High-rate engineered systems that provide reliable and efficient performances. Installations with metal recovery capacities of a few kilograms up to 24 ton/d have been built.
Metal removal and recovery cases
Zinc refinery free of solid waste ...