265300 Production of Novel Adsorbents From Waste Electric and Electronic Equipments
The problems regarding ecosystem contamination are increasing with expansion of the technology. Among these problems, toxic heavy metal pollution in air, soil and water is one of the foremost global problems and is a great threat to humanity. Toxic metal compounds coming to the earth's surface not only reach the earth's surface waters, but can also contaminate underground water by leaking from the soil after rain and snow. Therefore, the earth's waters may contain various toxic metals which might result in drinking water contamination and thus poisoning due to bioaccumulation. Bioaccumulation is an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are excreted or metabolized. In response to the ever-growing problems, federal and state governments have instituted environmental regulations to protect the quality of surface and ground water from heavy metal pollutants, such as Pb and Zn.
A number of methods for the removal of heavy metals from dilute aqueous solutions have been reported, including a reduction process, sulfide treatment, ferrous chloride treatment, magnetic ferrites treatment, ion exchange and ion exchange followed by chelating resin. Among the several treatment technologies developed, adsorption has been found to be superior to other techniques for wastewater treatment in terms of simplicity of design, ease of operation and insensitivity to toxic substances. In general, activated carbons are extensively-applied effective adsorbents for wastewater treatment. Nevertheless, the high cost of commercial activated carbon has led to hunting for more economical sources for the raw material to reduce the capital cost. Among these, agricultural waste based activated carbons are of great interest nowadays. Several researchers have studied the production of activated carbon from Ceiba pentandra hulls, pecan shell, hazelnut shell, peanut hull, almond shell, peach stone and sawdust.
To the best knowledge of the authors, no report has been published about the use of non-metallic fraction of Waste Electric and Electronic Equipments (NM-WEEE) as adsorbents in order to remove the metal contaminants from the dilute aqueous solutions. Since these materials contain a considerable amount of silicon, alumina, and carbon, all of which have a high potential to be good adsorbents when treated well, they were chosen to be our research target. Another reason for opting for these materials is that during the recent years, there is an ever-increasing concern about management of this waste and lack of proper methodology for its disposal. The two prevalent methodologies applied to this waste are either incineration or landfilling both of which have been hindered due to the evolution of potent toxic gases in the case of former technique and lack of enough land space and toxic contamination of the land in the case of later technique. Without the systems and the technology in place to effectively capture and manage these wastes, the accumulation of e-wastes has and will continue to be a significant problem at a global level. The rate of increase in the volume of e-waste now far exceeds the generation of municipal waste.
Preliminary experiments showed that untreated NM-WEEE is a very hydrophobic material with a trivial surface area. Therefore, it was expected that this material could not be used as an adsorbent in wastewater treatment despite its potentiality in terms of its constituent components. Hence, to facilitate the adsorption and development of porosity, chemical modification was carried out by the impregnation of the precursor in KOH for 3hr followed by pyrolysis in an inert atmosphere at 250˚C for 3hr. Although the surface area of the material was increased from 2 m2/g to 240 m2/g after modification, a high metal removal efficiency could not necessarily be guaranteed. Thus, a full adsorption test was carried out by using modified NM-WEEE as adsorbent and copper ions as adsorbate. The results indicated a significant amount of adsorption which was 3 mmol/g in comparison with 2.2 and 2mmol/g for its famous industrial counterparts, i.e. Suqing D401 and Lewatit TP207, respectively. The study was extended for two more metal ions, that is Zn and Pb. In the case of Zn, our novel adsorbent could adsorb 2.5 mmol/g, whereas this amount was only 1.9 and 1.6 mmol/g of Suqing D401 and Lewatit TP207, respectively. For Pb-bearing effluent, the adsorption is even more encouraging which shows an adsorption capacity of 3.5, 2.3 and 2.2 for our novel adsorbent, Suqing D401 and Lewatit TP207, respectively. All these figures indicate the extraordinary efficiency of the innovatively synthesized material to treat the wastewater effluents containing metal ions.
In terms of financial aspects, it is notable that since the precursor is a waste material and the treatment temperature is very low compared to the ones in the normal modification processes in the industry (600-1000˚C), the production cost will be reduced enormously.
To conclude, the production of this novel adsorbent could environmentally be of great interest in two points of views: on one hand, this waste (WEEE) can cause serious environmental contamination problems and this finding can beneficialize this material’s usage. On the other hand, this synthesized material can be employed to remove the heavy metal ions from the effluents causing ecological concerns.
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