Recovery of high purity zinc from filter ash produced during the thermal treatment of waste and inerting of residual materials

Abstract

The method described below recovers zinc, a valuable metal that is present in high concentrations in filter ash from the thermal treatment of waste, and returns the filter ash stripped of heavy metals to the combustion process in order to destroy organic substances. On an industrial scale, the heavy metals in the filter ash were mobilized by means of hydrochloric acid in the acidic fluids produced in the flue-gas scrubbing process without the addition of further chemicals. A pilot plant for implementing the selective reactive extraction (SRE) method on the ash extracts, using a highly selective complexant, was operated over a period of several months in order to obtain a concentrated, high-purity zinc salt solution (mono metal solution). A zinc depletion rate of 99.8% in the aqueous extract was achieved using mixer-settler units. The residual zinc concentration in the waste water was then < 2 mg L(-1). By stripping the loaded organic phase, a concentrated, high-purity mono metal solution with 190 g L(-1) zinc was obtained. Zinc metal with a purity > 99.99% is then separated by means of electrolysis. To destroy organic substances present in the filter ash, particularly dioxins and furans, the extracted filter ash cake was returned to the combustion process together with household waste. Plant operation, raw and pure gas parameters, and quality of the bottom ash produced were not impacted by such recirculation. The profitability of the overall process is attributable both to the recovery of valuable zinc metal and to the cost savings made in waste water treatment and in the disposal of the waste combustion residues because the remaining mixture of filter ash and bottom ash can be reused in a combined form. This method therefore supports the sustainable and economically viable reuse of filter ash.

Bioelectrochemical recovery of Cu, Pb, Cd, and Zn from dilute solutions

“…From these leachates metals could be recovered using e.g. solvent extraction and electrolysis [17,18], but the high energy consumption of electrolysis is an important factor for the profitability.…”

What is Required for the Viability of Metal Recovery from Municipal Solid-Waste Incineration Fly Ash?

“…On the other hand, because only a few species, mainly Ba, do not fulfil leaching limits in our tests, a further development of the leaching process and/or rest ash handling may make possible a local disposal also of the rest ash, and consequently avoidance of all the transport to Langøya, saving money, energy and CO 2 . A three times higher investment cost, as suggested for a zinc extraction plant with similar metal recovery, but, due to higher metal concentration in that case, almost a factor of ten less treated fly ash [21], lowers the NPV by 20 million SEK. Such an increase in plant investment cost may still give a positive NPV, though.…”

“…p) The value for zinc production in a corresponding process adjusted for the lower standard potential in Cu reduction is used [21]. This also corresponds to data (8 GJ/ton Cu) for large-scale Cu electrowinning in mining industry [39]; q) Average values for Chilean electrorefined (i.e., pyrometallurgical) copper cathodes in 2008.…”

“…[20]. Quite recently, investigations of the applicability of hydro metallurgic methods to recover metals from MSWI ash have started [21][22][23]. Providing that the metal compounds present in the ash can be dissolved in, for example, an acid, either solvent extraction or electro chemical processes can be used to separate the metals into pure forms.…”

Effect of Environmental Pollution on Production and Metabolic Profile in Buffalo Cows

“…Some metals act as catalysts for dioxins and furans synthesis [8] actually providing a surface for a rapid formation of these compounds. According to the WHO (World Health Organization), metals of most immediate concern are chromium, zinc, iron, mercury and lead; zinc is a trace element essential in quantities exceeding any other trace element, besides iron, it is known for its protective properties against diseases and is also very important for immune system.…”