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University of Vigo posted this:

Many industries, such as those belonging to the textile, wine, and paper industry, consume huge volumes of water and, as a result, generate a large amount of contaminated water containing persistent colour pollutant compounds. These compounds represent an environmental and health threat due to their well-known associated problems, such as carcinogenicity, toxicity and mutagenicity. Furthermore, they entail a great environmental impact when discharged in aquatic environments, perceptible at very low concentrations, creating an undesirable visual impact, which, in many cases, does not meet the degree of conformity under the current directives on the wastewater treatment for industrial effluents (Directive 91/271 / EEC). The solution proposed by the research group Chemical Engineering at the University of Vigo, is the use as adsorbent of peat, or a similar lignocellulosic material, immobilized in calcium alginate beads. This process is efficient, cheap and environmentally friendly, unlike other processes and technologies. In fact, the utilization of peat instead of activated carbon as industrial adsorbent has the advantage that peat requires no activation, unlike activated carbon, reducing operating costs. In addition, the low cost of the adsorbent would be translated into significant economic benefits. Moreover, depending on the contaminant removed from the waste effluent, the exhausted adsorbent may be used as soil fertilizer at its end of life.


This method has two stages: 1) Dispersion of, at least, an inorganic material in water. 2) Addition of, at least, an organic coloring solubilized by agitation. The following parameters might be changed in order to obtain different kinds of nanopigments: • Inorganic material concentration. • Organic coloring concentration. • pH. • Temperature. • Ionic strength. The optical response of nanopigments changes as a function of the particle size of the inorganic material (or materials) used by the diffusion. This method makes it possible to produce new hybrid nanopigments with optical and colloidal properties for tailored applications. Mainly, the customizaton of the behaviour of this materials is achieved by controlling organic/inorganic ratio in the material. The morphology of the material is hybrid (laminar/fibrillar). The organic coloring is selected among different types: azoic complexes, metallic, sulphurose, iminoquinone, antraquinone, ftalocianine, etc. In general words, they can be both natural or synthetic. Products can be used in printing inks, painting and dyes, paper, synthetic or natural fibers, polymer materials, cosmetics, etc. With this method the following features can be achieved: Color range control: Through the control over the different spectral species, the optical response is modified too, so the color range can be enlarged. Increase in the colouring power: The ability of the material for increasing the absorption on the surface is linked to three parameters. First, absorption coefficient of the nanopigment in relation to the coloring solution coefficient. Second, light dispersion caused by nanoparticles and addtiional coverage of the surface to fill. Third, reology and fisico-chemical properties of the material are able to obtain homogeneous dispersions. Environmental impact reduction: Some of the usual pigments contain heavy metals in its composition while inorganic solids used in this method are free of heavy metals and can even be used in cosmetics. Natural coloring can be combined with these nanopigments and obtain a new product which will be environmental safe.