Pilot-Scale Decontamination of Soil Polluted with As, Cr, Cu, PCP, and PCDDF by Attrition and Alkaline Leaching

Abstract

Recently, an efficient and promising process was developed to allow the removal of As, Cr, Cu, pentachlorophenol (PCP), and 7 polychlorodibenzo-dioxins and furans (PCDDF) from soil using alkaline leaching. The present study evaluates the performance and the 8 robustness of this decontamination process for the treatment of four different polluted soils by attrition and alkaline leaching at a pilot scale. 9The attrition process carried out on the coarse fraction (>0.125 mm) allowed the removal of 24-42% of As, 0-13% of Cr, 23-46% of Cu, 0-10 85% of PCP, and 17-64% of PCDDF from the different contaminated soils. Removal yields of 87-95% of As, 50-72% of Cr, 73-84% of Cu, 11 52-100% of PCP, and 27-73% of PCDDF were obtained after three leaching steps (½NaOH ¼ 1 M; ½Cocamydopropylbetaine-BW ¼ 3% 12(w/w); t ¼ 2 h; pulp density ½PD ¼ 10% [w/v]) conducted on the fine fraction (<0.125 mm). The performance of both attrition and alkaline 13 leaching processes seemed to be influenced by the nature of the soil and the type and initial level of contaminants present in the soils.14 However, the entire leaching process seemed to be highly efficient, allowing the simultaneous reduction of concentrations of inorganic 15 and organic contaminants. The cost, including direct and indirect costs, were estimated between US$214 and 454 per ton of treated soil, 16 depending on the nature of the soil and the initial level of contamination.

Counter-Current Attrition Process (CCAP) to Remove Metals, Pentachlorophenol (PCP), Dioxins and Furans (PCDDF) from the 1-4-mm Fraction of Contaminated Soil

“…Over the past several decades, several authors have studied physical and chemical decontamination processes to evaluate their ability to simultaneously remove inorganic and organic compounds from solid matrices, including soils (Riveiro-Huguet and Marshall, 2011;Bisone et al, 2013a;Reynier et al, 2013a, b;Guemiza et al, 2016;Metahni et al, 2016). The attrition uses high-intensity agitation to remove films around soil particles and/or to detach fine particles from the surface of coarse particles, resulting in the release of contaminants.…”

“…The attrition process is governed by the physical contact between the contaminated particles themselves, the contact between the contaminated particles and the liquid phase, and the walls and the impellers present in the mixing reactor, which favor the removal of the fine particles that contain the contaminants. As most of the contaminants present in soil usually have low water solubility, such additives as acids, alkaline agents, surfactants and/or chelating agents are often added into the attrition pulp to improve the removal of both inorganic (e.g., As, Cr, Cu, Pb, and Zn) and organic compounds (e.g., PAHs, PCP, and PCDDFs) (Riveiro-Huguet and Marshall, 2011;Bisone et al, 2013a;Reynier et al, 2013b;Guemiza et al, 2016;Metahni et al, 2016). Surfactants are compounds that contain both hydrophilic and hydrophobic parts in their molecular structure.…”

Influence of Soil Parameters on the Efficiency of the Attrition Process to Remove Metals, PCP, Dioxins and Furans from Contaminated Soils

“…Another parameter that could influence the performance of an attrition process is the stirring speed. A study carried out at room temperature showed that three attrition steps of 20 min each performed at 1,700 rpm with a pulp density fixed at 40% (w/w) allowed the removal of 24 -42% of As, 0 -13% of Cr, 23 -46% of Cu, 0 -85% of PCP and 17 -64% of PCDD/F from the coarse particles (> 0.125 mm) of contaminated soils (Metahni et al 2016). The attrition tests carried out by Bayley et al (2005) with an aqueous suspension of contaminated soil showed that the speed of the impeller had a significant effect on the removal of contaminants.…”

“…Bisone et al (2013) removed more than 90% of PAHs from soils using attrition in the presence of a surfactant ([Cocamidopropyl Hydroxysultaine, CAS] = 0.2 g.L -1 ). Metahni et al (2016) found that three attrition steps (PD = 40%, T = 25°C, 1-4 mm soil fraction) allowed the removal of 60% and 97% of PCP with and without the addition of surfactant (cocamidopropylbetaine, BW) at 1% (w.w -1 ), respectively. Recently, Guemiza et al (2016) showed that the concentration of the surfactant BW (0 -3%, w.w -1 ) was the main parameter influencing the removals of both PCP and PCDD/F from the 1-4 mm soil fraction by attrition (PD = 40%, T = 25°C, t = 20 min, 5 attrition steps), using an experimental design methodology.…”

“…Attrition was found to be an efficient technique (INRS-Georessources & CRM 1997). This technique can be used as a physical decontamination process alone (Bayley et al 2005;Bisone et al 2013;Guemiza et al 2016;Metahni et al 2016;Stražišar and Sešelj 1999) as well as a step prior to other decontamination processes such as gravity concentration and froth flotation (Bisone et al 2012;Jobin et al 2015Jobin et al , 2016Veetil et al 2014;Williford et al 1999). Attrition scrubbing allows friction between contaminated particles; enhancing the removal of the thick films around soil particles and/or the detachment of fine particles usually contaminated from the surface of the coarse particles (uncontaminated).…”