New Technologies in the Mining Industry Wastewater Treatment

Waste water from mining industry shows a wide spectrum of compositions. Many of the components present in waste water from the iron and steel industry are also often present in the water from the mining industry. The waste water from flotation and enrichment of lead and zinc ores, which in addition to components present in waste water from other mining industries also contain xanthate, zinc and lead. Mine wastewater primarily contains heavy metals, cyanide and secondary treated sewage. IronSulphateCalciumAl3+pH (2.0-3.0)This section provides details on the latest developments and efforts in the Mining industry waste water treatment.

We have discussed the following:Current Wastewater Treatment Process - Mining IndustryNew Technologies in the Mining Industry Waste Water TreatmentTailing PondsChemical and Biological Methods

Current Wastewater Treatment Process - Mining IndustryAmmoniacal leaching is pretty old and proven technology in the mining industry, having been used for over 80 years, mostly for copper recovery (either metallic copper or copper sulfide with oxidation) but also for nickel and cobalt recovery (after reduction roast, with oxidation). The selectivity it provides over other metals is exactly why it has been used. In fact, as far as hydroxide sludges, there is a big Australian nickel/cobalt project (the Cawse project owned by Centaur Mining) suffering through startup woes right now in which they do an autoclave acid leach to get everything into solution, then partially neutralize it to get rid of iron etc., then precipitate a Ni/Co.Ammoniacal leaching process is employed to remove metals (specifically Copper, Zinc, Nickel, Cobalt, and Cadmium) from mining industry wastewater.1Other wastewater treatment systems include,ThickenersClarifiersDewatering systemsBiological treatmentMicrofiltration Reverse OsmosisMine drainage treatment systemsIon exchange (metals and traces contaminant removal)New Technologies in the Mining Industry Waste Water TreatmentThe section below focuses on the recent developments in the mining industry wastewater treatment with tailing ponds and other chemical and biological methods.Tailings PondsTailings are the materials left over after the process of separating the valuable fraction from the worthless fraction of an ore. The extraction of minerals from ore requires that the ore be ground into fine particles, so tailings are typically small and range from the size of a grain of sand to a few microns. Mine tailings are usually produced from the mill in slurry form.2Chemical and Biological Treatment of Mining WastewaterAcid-rock drainage (ARD) also known as acid-mine drainage (AMD) results from the exposure of sulfide minerals, particularly pyritic and pyrrhotitic minerals, to atmospheric oxygen and water. The most common is the chemical precipitation using lime or other basic substances. These systems produce large volumes of wet sludge that often require drying facilities to concentrate the metal hydroxide sludge. Recent developments and improvements have resulted in construction of bioreactors that have a smaller footprint, and treat the metals and acidity more effectively.Oxyanions such as chromate and arsenate can be removed using the wetland treatment system (passive bioreactor) technology. Arsenic is removed as an arsenic sulfide compound and chromate is reduced to Cr(III) and precipitated as a hydroxide. The passive Bioreactor wetland treatment system offers a less expensive alternative to the conventional chemical precipitation technologies. There still are problems of system hydraulics and useful life to be addressed.Biological MethodsMany studies have demonstrated that the primary removal mechanisms for the metals are sulphate-reducing bacteria (SRB). These microbes facilitate the conversion of sulphate to sulphide. The sulphides react with metals to precipitate them as metal sulfides, many of which are stable in the anaerobic conditions of the treatment system. The SRB are obligate anaerobes which prefer conditions between pH 5 and 8. Low pH waters do reduce the capacity of the treatment systems to treat metals effectively. Plants have been shown to remove metals by uptake or oxidative precipitation near the roots.3Sulphate-reducing biofilm and suspension processes were studied for treatment of synthetic wastewater containing sulphate, zinc and iron. The results of this work demonstrate that the lactate supplemented sulphate-reducing processes precipitated the metals as sulphides and neutralized the acidity of the synthetic wastewater (Kaksonen et al.,).