Inertization of Heavy Metals Present in Galvanic Sludge by DC Thermal Plasma

Abstract

Galvanic sludge results from the treatment of effluents generated by the industrial metal surface treatment of industrial material, which consists in the deposition of a metal on a surface or a metal surface attack, for example, electrodeposition of conductors (metals) and non conductive, phosphate, anodizing, oxidation and/or printed circuit. The treatment proposed here is exposure of the galvanic sludge to the high temperatures provided by thermal plasma, a process which aims to vitrify the galvanic sludge and render metals (iron, zinc, and chromium) inert. Two different plasma reactors were assembled: with a DC transferred arc plasma torch and with a DC nontransferred arc plasma torch. In this way it was possible to verify which reactor was more efficient in the inertization of the metals and also to investigate whether the addition of quartzite sand to the sludge influences the vitrification of the material. Quantification of water content and density of the galvanic raw sludge were performed, as well as analyzes of total organic carbon (TOC) and identify the elements that make up the raw sludge through spectroscopy X-ray fluorescence (XRF). The chemical composition and the form of the pyrolyzed and vitrified sludge were analyzed by scanning electron microscopy with energy-dispersive X-ray spectrometer (SEM-EDS) analysis, which it is a analysis that shows the chemical of the sample surface. The inertization of the sludge was verified in leaching tests, where the leachate was analyzed by flame atomic absorption spectroscopy (FAAS). The results of water content and density were 64.35% and 2.994 g.cm(-3), respectively. The TOC analysis determined 1.73% of C in the sample of galvanic raw sludge, and XRF analysis determined the most stable elements in the sample, and showed the highest peaks (higher stability) were Fe, Zn, and Cr. The efficiency of the sludge inertization was 100% for chromium, 99% for zinc, and 100% for iron. The results also showed that the most efficient reactor was that with the DC transferred arc plasma torch and quartzite sand positively influenced by the vitrification during the pyrolysis of the galvanic sludge.

Thermal Plasma Treatment of Medical Waste

“…Therefore, in order to obtain slags for utilization, it is needed to optimize the addition of additives. For other hazardous wastes, SiO 2 content has been proven to enhance the plasma vitrification process [40,98,104]. It can result in the domination of SiO 4 tetrahedron inside the vitrified slag, and thus traps metals [105].…”

“…For other hazardous wastes, SiO 2 content has been proven to enhance the plasma vitrification process [ 40 , 98 , 104 ]. It can result in the domination of SiO 4 tetrahedron inside the vitrified slag, and thus traps metals [ 105 ].…”

“…However, high temperature also means more heavy metals will volatilize to the gas phase. A number of studies have reported the volatilization of heavy metals in plasma treatment of various waste streams [ 40 , 108 – 110 ]. Although the percentage of metals in medical waste may be lower, it can not be neglected.…”

“…Faced with these problems, thermal plasma technology for treat solid wastes is recognized worldwide as being highly efficient and it has been used for the elimination or Table 1 Comparison between thermal treatment processes of medical waste [2,5,12,[50][51][52][53][54][55][56] transformation of different types of waste including plastics waste [22,23], waste tires [24][25][26], biomass [27][28][29], municipal solid waste [15,30,31], electronic waste [32][33][34], fly and bottom ash [35][36][37][38][39], municipal and industrial sludge [40][41][42][43][44]. Plasma methods are not only used for the production of fuel gas but also appear to be high potential to produce glass-like slag that can be utilized or from which to recover metals [45,46].…”

Possibilities of zinc extraction from galvanic sludges by means of electrolysis

“…At the Northeast Normal University, China, the galvanic sludge re-use for a preparation of new adsorbents for waste water treatment has been brought into focus [9]. Galvanic waste processing through a vitrification method is described in [10,11]. A lot of researches have been oriented on re-gaining of different metals from the galvanic sludge, e.g.…”