CSP Science

CSP to recover zinc from steelworks waste PDF Imprimer Envoyer
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Jeudi, 27 Février 2014 09:34

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Switzerland is not the kind of country you would think about to deploy Concentrated Solar Power systems, but the Paul Scherrer Institute (PSI), located in the idyllic northern city of Villigen, is working on CSP developments since the beginnings of the CSP era.

 

lll.jpgThe PSI has announced that a researchers team has showcased a solar-thermal method for extracting zinc oxide, a technologically important reusable material, from zinc recycling products under laboratory conditions. The announcement remarks that the solar product’s purity level exceeds that obtained via the industrially established route.

Zinc is one of the most important reusable materials of the modern world and is widely used for a number of applications, although the majority of global zinc production is intended for corrosion protection. Indeed, every year, millions of tons of steel are zinc-coated to make it weather-proof, such as for vehicle bodies.

Steelworks are the main source of secondary raw materials (i.e. not from mineral ores) for the production of zinc. Up to 35% of dust accumulated in filters while recycling galvanized steel is zinc in electric arc furnaces and  roughly 40% of the 7 million tons of electric arc furnace dust accumulated every year is processed further for the purposes of zinc recovery.

Recovering zinc

The most common way to recover zinc oxide from filter dust is the so called Waelth method, where the zinc oxide is reduced to zinc in a chemical process to obtain crude 'Waelz oxide' which is then washed to remove fluorine and chlorine impurities to reach a 80% purity zinc oxide.

The research conducted by PSI has demonstrated a solar-thermal method to purify the Waelz oxide under lab conditions. The project was carried out in collaboration with researchers from the University of Leoben in Austria and industrial partner Befesa Steel AG.

The team has used unwashed Waelz oxide as based material. The oxide to be purified was processed in a solar reactor, which was heated with concentrated radiation from the PSI’s own high-flux solar simulator, in which ten xenon lamps serve as the radiation source. With the aid of mirrors, the xenon-lamp light is concentrated to several thousand times the solar radiation density that reaches Earth. Exposed to the concentrated radiation from five of these artificial suns, the Waelz oxide was heated to 1,300 degree Celsius in order to evaporate off the undesired lead and chlorine compounds, thereby purifying the Waelz oxide.

The solar reactor used by the researchers has two chambers. The concentrated radiation enters the upper chamber (1) via the entry window (made of quartz)(2) and heats the partition between the chambers. The heated separation wall (3) then radiates the majority of the energy absorbed into the lower chamber (reaction chamber)(4), where the actual chemical reactions take place. This separation makes sure that evaporated gas or rogue particles in the reaction chamber leave the reactor through the exhaust pipe (5) instead of reaching the quartz window and accumulating on it as solid residues, which would absorb the incident radiation, overheat the entry window and potentially damage it. The problem of window contamination is one of the biggest technical hurdles in upgrading this kind of solar reactor to an industrial scale. Source:Paul Scherrer Institute.

The solar reactor used by the researchers has two chambers. The concentrated radiation enters the upper chamber (1) via the entry window (made of quartz)(2) and heats the partition between the chambers. The heated separation wall (3) then radiates the majority of the energy absorbed into the lower chamber (reaction chamber)(4), where the actual chemical reactions take place. This separation makes sure that evaporated gas or rogue particles in the reaction chamber leave the reactor through the exhaust pipe (5) instead of reaching the quartz window and accumulating on it as solid residues, which would absorb the incident radiation, overheat the entry window and potentially damage it. The problem of window contamination is one of the biggest technical hurdles in upgrading this kind of solar reactor to an industrial scale. Source:Paul Scherrer Institute.

Drastic reduction in the lead content

The result of this “solar clinkering” was a success: better zinc oxide was produced from the crude Waelz oxide than that obtained through conventional industrial washing. In particular, the proportion of undesired lead plunged to under 0.1 per cent compared to around 5 per cent in the washed Waelz oxide.

Successful lead reduction is especially relevant when it comes to processing zinc oxide further into zinc as the electrolytic procedure used industrially does not handle even minor concentrations of lead very well. The solar-enhanced zinc oxide could also be reduced to zinc in the solar reactor via a reaction with carbon.

The PSI scientists conducted an earlier research for the so-called solar carbothermal reduction. the Solzon project: http://www.psi.ch/lst/solzinc

The results from this study are available at:

Thermal recycling of Waelz oxide using concentrated solar energy
N. Tzouganatos, R. Matter, C. Wieckert, J. Antrekowitsch, M. Gamroth, A. Steinfeld
JOM : Vol. 65. no. 12, Dec. 2013
DOI: 10.1007/s11837-013-0778-x

 
Content archived in: Technology & ResearchEurope

Content tagged with: PSIPaul Scherrer InstitutezincSwitzerland

Source: www.csp-world.com

 

Mise à jour le Jeudi, 27 Février 2014 09:49
 

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