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Solar detoxification of wastewater in the silversmith - goldsmith industry

To develop a new visible light active technology for water detoxification and precious metal recovery from wastewater in the silversmith - goldsmith (electroplating) industry.

Wastewaters containing heavy metal ions and toxic organic components are commonly generated in metallurgical and electroplating industries, in the manufacture of printed circuit boards, related items and other electronic components. The chemicals and heavy metals are usually toxic and thus cause aquatic and land biota to sicken or die. Most wastewater processing technologies that are currently available emphasise the removal of the chemicals or heavy metals as cautions. However, the anions associated with heavy metal cautions can be equally as toxic but are largely ignored. In this regard, the remediation of cyanides or both metals and cyanides can be considered very important. Cyanide (CN-) is a toxic species that is found predominantly in industrial effluents generated by metallurgical and electroplating operations. Cyanide's strong affinity for metals makes it favourable as an agent for metal finishing and treatment and as a lixivant for metal leaching, particularly gold. Today much is being done in the EU to see to it that the electroplating industry eliminate all the toxic components from its wastewater. Conventional treatment involves hydroxide precipitation resulting in toxic sludge which must be disposed off by landfill, an increasingly expensive option. TiO2 photocatalysis for the reclamation of metals from industrial wastewater using TiO2 powder in slurry type reactors has been investigated. However, metal ion solutions effectively screen the TiO2 catalysts from the incident light source, and the direct reaction of metal ions with organic compounds present may result in lower process efficiencies. Therefore the development of an effluent treatment stage, which reduces the total organic carbon (TOC) loading and simultaneously recovers heavy (or precious) metals, is an important step for industrial wastewater treatment technology. An experimental and industrial solution for the above problem is part of the present proposal. The project is focusing on developing a new visible light photocatalytic technology, materials, process and system for water detoxification and precious metal recovery. In the electroplating industry, liquid waste comes mostly from the coating process of precious metal artefacts. Effective treatment of the liquid waste from the coating process is called for, in order to recover precious metals and eliminate toxic organics contained in the wastewaters. It is well known that the major problem of the organic compounds relates to the toxic cyanides ions whose drainage in the public sewerage system is detrimental to the land. The alternative drainage directly to the ground causes major pollution in ground water. The addition of fresh drinking water in cyanide containing wastewater and following drainage in the public sewerage system is the most common way for cyanide 'elimination' nowadays. However it does not improve environmental management because the exact same quantities of cyanides are falling onto the ground. The mechanism for removing organic cyanides and for metal reduction can be represented as follow. Anode: TiO2 + 2hv = TiO2 (hv+ +2e-) surface 0.5 O2 + 2e- + H2O = 2OH- 2OH-+2h = 2OH- CN-+ OH = OCN- +H2O 2OCN- +O2=2CO2 + N2 Overall reaction 2CN-+O2+(hv)=2CO2+N2 the reduction of metals at the cathode can be described by the following reaction Cathode: Me1+ + 1e- -> Me 0 The aim of the project will be achieved with the: * Development of photocatalytic materials with improved properties in visible light. * Design of a visible light active photocatalytic reactor. * Laboratory experiment testing for purification of polluted industrial water. * Solar Detoxification System (SDS) - Photocatalytic device - construction for wastewater detoxification including cyanide degradation and precious metal recovery. Novel visible light active photocatalytic materials based on TiO2 doped by nitrogen or fluorine will be developed. The photocatalysts will be studied in industrial catalytic processes like the decomposition of pollutants in wastewater. The TiO2 doped by nitrogen, fluorine, etc., will prepared in the form of nano-structured coatings supported on a transparent substrate. The intermediate and final products of N (F)-doped titania will be characterised from the viewpoint of the structure, surface area chemical stage of surface and near surface layers. The conditions for the preparation of N (F)-doped titania with improved photocatalytic properties will be investigated. The effect of the doping situation such as the position of the dopants in the lattice or on the surface of TiO2-xNx (TiO2-xFx) nano-particles and the homogeneity of the dopant distribution on the photocatalytic activity will be studied by TEM (Transmission Electron Microscopy), AFM (Atomic Force Microscopy) microscopy and RBS (Rutherford Backscattering Spectrometry) and XPS (X-ray Photoelectron Spectrometer) spectroscopies. The coatings will be used for construction of a photo-reactor for the treatment of contaminated water under UV (Ultra-Violet) and visible light irradiation. A two-compartment photoelectrochemical cell for decomposing the cyanide pollutants in the anode and recovering the precious metals in the cathode compartment will be used for experimental investigations. The simultaneous photocatalytic oxidation of organic pollutants in the anode and the reduction of metal ions in the cathode are expected to have application potential especially in GREECE and other European countries where solar illumination can be used.
Acronym: 
DETOX
Project ID: 
3 512
Start date: 
01-09-2003
Project Duration: 
36months
Project costs: 
1 800 000.00€
Technological Area: 
Recycling, Recovery
Market Area: 
Chemical and solid material recycling

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.