Search

Serpentinite tailings from La Nationale chrysotile mine in Thetford Mines (Quebec, Canada) were studied to extract the Mg contained therein. The study began with an initial chemical characterization of the residue to determine the Mg concentration in the different grain size fractions. The resulting Mg-containing fractions were leached under a variety of parameters such as type of acid, acid concentration, treatment time, and temperature, and the obtained solution was neutralized with NaOH for the selective recovery of the metals. The results of this study were used to design a process to obtain Mg as a marketable chemical. The tested process consists of a leaching step using an H2SO4 solution followed by the purification of the leachates using NaOH at pH 8 and Mg recovery with NaOH at pH 10. A final product composed of mirabilite (Na2SO4) and brucite (Mg(OH)2) was obtained. The procedure was tested, and its economic viability was discussed. The approach proved to be technically feasible, promoting clean production. [ABSTRACT FROM AUTHOR]

This research work focuses on the development of a new process for the decontamination of municipal wastes incinerators fly ashes. The objective of this study was to evaluate different total and selective precipitation methods for metals removal from ash decontamination leachates. The tested options include 1) use of hydrated lime and caustic soda for selective (pH 5.0) and total (pH 8.5) metal precipitation; 2) addition of different chemicals (H3PO4, Na2S and FeCl3) in a pH range from 6.0 to 9.0. Fly ash decontamination assays using alkaline and acid washing steps were initially performed using optimal conditions previously established. Treated fly ashes respected the standards based on the TCLP leaching test for all studied metals and SPLP. Total metal precipitation tests carried out at pH 8.5 achieve removal yields for all metals ≥ 90% using hydrated lime and ≥ 83% using caustic soda. Selective precipitation tests alone at pH 5.0 show removal yields ≥ 97% for Cr and between 75 and 87% for Al and Pb. Moreover, assays carried out using a stoechiometric addition of Na2S have allowed the separation of Cd (≥ 99%) and Zn (≥ 71%) as metal sulphides (CdS and ZnS). From an economical point of view, the most interesting option seems to be the leachates neutralization at pH 7.0 using Ca(OH)2 combined with the reuse of the treated leachates in the fly ash leaching steps. Metal precipitation cost at pH 7.0 has been estimated to be 22.7 CAN$ tct-1 using Ca(OH)2, and 26.7 CAN$ tct-1 using NaOH. [ABSTRACT FROM AUTHOR]

An investigation on the effect of sludge solids concentration on bioleaching of Cr(III) and other metals from tannery sludge by indigenous sulphur-oxidizing bacteria was carried out. The sludge solids concentrations ranged from 13 to 60 g/L. The concentration of elemental sulphur was fixed at 30 g/L. The results showed that the lowest pH reached after 25 days of bioleaching at all studied sludge solids concentration was about 1.3. The optimum sludge solids concentration for maximum metal leaching from tannery sludge was 40 g/L and about 87% of Cr(III), 73% of Al, 72% of Fe, 62% of Mg, and 73% of Zn could be leached in this case. During bioleaching, the concentrations of total and volatile suspended solids of the tannery sludge significantly decreased. The sulphur-oxidizing bacteria could tolerate a Cr(III) concentration as high as 5,930 mg/L at pH 1.3. The leaching efficiencies of Cr(III), Al, and Fe for both chemical leaching and bioleaching of tannery sludge were similar at pH 1.3. The leaching efficiency of Ca, Mg, and Zn in both leaching processes were identical for pH values in the range of 1.3 to 3.0. [ABSTRACT FROM AUTHOR]

The MUC (Montreal Urban Community) treatment plant produces approximately 270 tons of dry sludge daily (270 tds/day) during the physico-chemical treatment of wastewater. Recently, this treatment plant endowed a system of drying and granulation of sludge for valorization as an agricultural fertilizer having a capacity of 70 tds/day (25% of the daily sludge production). However, the metal content (mainly Cu and Cd) of the sludge surpasses the norms for biosolids valorization. In order to solve this problem, a demonstration project, from the lab scale to the industrial pilot plant, was carried out to test the Metix-AC technology for the removal of metals. A strongly metal-loaded filtrate was generated during the sludge decontamination. Tests concerned the study of the metal recovery by total precipitation and selective precipitation, as well as the use of alternative products for the metal precipitation. Other works consisted to simulate the acid filtrate recirculation from the decontaminated sludge (25% of the total volume) in the untreated sludge (75% of the total volume) intended for the incineration. The total precipitation with hydrated lime appeared effective for the recovery of metals (87% Cd, 96% Cr, 97% Cu, 98% Fe, 71% Ni, 100% Pb, 98% Zn). However, this option entails the production of an important quantity of metallic residue, which should be disposed of expensively as dangerous material. The selective iron precipitation does not appear to be an interesting option because the iron in solution within the leached sludge was principally present in the form of ferrous iron, which cannot be precipitated at pH lower than five. On the other hand, the use of commercial precipitating agents (TMT-15, CP-33Z, CP-NB and CPX) without pH adjustment of filtrate gave good results for the recovery of Cu and, to a lesser degree for the recovery of Pb. However, the efficiency for the other metals' (Cd, Cr, Fe, Ni and Zn) recovery was weaker (< 25%). Finally, the acid filtrate recirculation containing solubilised metals in untreated sludge destined for incineration appears to be the most interesting option. Metals in solution in the acid filtrate, precipitate or adsorb effectively (97% Cd, 97% Cr, 99% Cu, 82% Ni, 100% Pb and 87% Zn) on the solids of the untreated sludge. Moreover, TCLP tests were done on ashes produced during the incineration of sludge mixed with the acid filtrate produced during sludge decontamination. These tests showed that there were no significant differences, as regards the extractability of metals, between such ashes and those produced during the untreated sludge incineration without addition of filtrate. Therefore, it was predictable that this method can respect the current environmental standards required by the different governmental authorities. [ABSTRACT FROM AUTHOR]

The objective of this research was to compare the efficiency of different natural adsorbents for lead recovery from basic leachate produced during municipal incinerator used lime decontamination. Shake flasks adsorption tests have shown that cedar barks, pine barks, cocoa shells, and peat moss are efficient and cheap adsorbents for lead removal from this type of leachate. Peanut skins are less efficient than other tested natural materials. The use of a hot-acid treatment (H[sub 2] SO[sub 4] 0.75 M) allows to slightly increase lead removal performance of the adsorbents. However, this gain does not justify, from an economical point of view, the utilization of the chemical treatment. Tests done with different cedar and pine bark concentrations (2–30 g/L) have revealed that heavily lead-contaminated (approximately 130–140 mg/L) used lime leachate can be efficiently treated by addition of a small adsorbent concentration (e.g. 2 g/L). Finally, elution tests (HCl 0.5 M) with reuse of adsorbents have demonstrated that some natural materials, like cedar barks and cocoa shells, can be used for many adsorption–elution cycles without loss of lead removal efficiency. Key words: lead, adsorption, used lime, leaching, peat, bark.[Journal translation]Cette recherche visait à comparer l'efficacité de divers adsorbants naturels pour la récupération du plomb extrait par lessivage basique de chaux usées d'incinérateur de déchets municipaux. Les tests d'adsorption effectués en fioles agitées ont montré que les écorces de cèdre, les écorces de pin gris, les écailles de cacao, ainsi que la tourbe de sphaigne sont des adsorbants efficaces et peu coûteux pour l'enlèvement du plomb de ce type d'effluent très basique. Les écailles d'arachides se sont avérées moins efficaces que les autres adsorbants testés. L'application d'un pré-traitement acide (H[sub 2] SO[sub 4] 0,75 M) à chaud permet d'accroître légèrement les rendements d'élimination du plomb des adsorbants. Les gains obtenus ne justifient toutefois pas l'utilisation de ce traitement chimique. Les tests effectués avec diverses concentrations (2 à 30 g/L) d'écorces de pin gris et de cèdre ont montré qu'il est possible de traiter efficacement les lixiviats de chaux usées chargés en plomb (environ 130 à 140 mg/L) par un apport de faibles quantités d'adsorbants, soit de l'ordre de 2 g/L. Finalement, des essais d'élution (HCl 0,5 M) et de réutilisation des adsorbants ont démontré que certains adsorbants, tels que les écorces de cèdre et les écailles de cacao, peuvent être employés pour plusieurs cycles d'adsorption–élution sans perdre leur capacité d'enlèvement du plomb. Mots clés : plomb, adsorption, chaux usées, lixiviation, tourbe, écorce. [ABSTRACT FROM AUTHOR]

Evaluates the efficiency of peat moss for lead and zinc recovery from alkaline leachates produced during decontamination of municipal incinerator fly ash. Measurement of the adsorption efficiencies of zinc; Initial metal concentrations in the leachates; Regeneration of peat moss for several adsorption cycles.