Study of the factors influencing the metals solubilisation from a mixture of waste batteries by response surface methodology.

This paper presents an innovative process for the recovery of valuable metals from a mixture of spent batteries. Different types of batteries, including alkaline, zinc-carbon (Zn-C), nickel cadmium (Ni-Cd), nickel metal hydride (Ni-MH), lithium ion (Li-ion) and lithium metallic (Li-M) batteries, were mixed according to the proportion of the Canadian sales of batteries. A Box-Behnken design was applied to find the optimum leaching conditions allowing a maximum of valuable metal removals from a mixture of spent batteries in the presence of an inorganic acid and a reducing agent. The results highlighted the positive effect of sodium metabisulfite on the performance of metals removal, especially for Mn. The solid/liquid ratio and the concentration of H2SO4 were the main factors affecting the leaching behavior of valuable metals (Zn, Mn, Cd, Ni) present in spent batteries. Finally, the optimum leaching conditions were found as follows: one leaching step, solid/liquid ratio = 10.9%, [H2SO4] = 1.34 M, sodium metabisulfite (Na2S2O5) = 0.45 g/g of battery powder and retention time = 45 min. Under such conditions, the removal yields achieved were 94% for Mn, 81% for Cd, 99% for Zn, 96% for Co and 68% for Ni.

Improvement of a three-step process for the treatment of aluminium hazardous wastes containing PAHs (benzo[b,j,k]fluoranthene and chrysene) and fluoride.

Hazardous wastes from a primary aluminium production plant could be decontaminated by a three-step process. First, the PAHs contained in these wastes were extracted with an amphoteric surfactant (0.25% or 0.50% w/w of cocamidopropylhydroxysultaine [CAS]) by cell or column flotation, depending on the particle size fraction (under or above 500 microm). Then, the fluorides were stabilized with lime (8% w/w) or a mixture of lime (4% w/w) and phosphoric acid (0.95% w/w). The decontaminated wastes satisfied the Quebec PAH norm, fixed at 1000 mg kg(-1), with values of 900 +/- 352 mg kg(-1) and 624 +/- 179 mg kg(-1) for benzo(b,j,k)fluoranthene (BJK) at laboratory and pilot scales, respectively. The fluoride stabilization in the treated wastes was characterized by TCLP values of 138 +/- 67 mg F- L(-1) and 29.5 +/- 7.6 mg F- L(-1) for laboratory and pilot experiments, which were under the Quebec norm (< 150 mg F- L(-1)). Finally, the metals in the process effluent were recovered by precipitation with sulphuric acid (10% v/v), and the final effluent and metallic residue obtained were recirculated without liquid fraction enrichment impact. The whole process was successfully tested at pilot scale. The preliminary economic study showed the potential of the process for the treatment of aluminium hazardous wastes.

Combined column and cell flotation process for the treatment of PAH contaminated hazardous wastes produced by an aluminium production plant.

The aluminium electrolytic plants generate PAH and fluoride contaminated wastes which are usually classified as hazardous material. These residues are generally disposed in secure landfill sites. A flotation cell process was previously developed to remove PAH from these aluminium industry wastes. The tests were done on composite samples made of particle size fractions under 50mm. The efficiency of the flotation cell process was demonstrated but the high quantity of concentrate produced (14.0%) during the air injection period, because of the solid entrainment, raised the treatment cost. The aim of this study was to reduce the entrainment of fine particles in order to obtain an efficient and economic technology. The process initially developed was modified: the smallest particle size fraction (<0.5mm) of the composite sample was treated in a flotation column, whereas the other particle size fractions (0.5-50mm) were treated in a flotation cell. The separated treatment allowed to reduce the entrainment during the air injection period of the flotation cell step from 14.0% to 10.1%. The optimum total solids of the pulp and cocamidopropylhydroxysultaine (CAS) concentration were 3.33% and 0.50% (ww(-1)) for the flotation column, and 15% and 0.25% (ww(-1)) for the flotation cell. This combined flotation process minimized the total entrainment which allowed a 23.6% abatement of the concentrate quantity initially produced, and reduced the PAH concentrations of the wastes under the authorized limit of 1000 mg kg(-1).

Pilot-plant study of wastewater sludge decontamination using a ferrous sulfate bioleaching process.

The objective of this research was to investigate the performance of the ferrous sulfate bioleaching (FSBL) process in a pilot plant for decontamination and stabilization of wastewater sludge. Batch and continuous experiments, conducted with two 4-m3 bioreactors using indigenous iron-oxidizing bacteria (20% v/v of inoculum) with addition of 4.0 g ferrous sulfate heptahydrate per liter of sludge initially acidified to pH 4.0, were sufficient for effective heavy metal (cadmium, copper, manganese, zinc, and lead) removal yields. The average metal removal yields during the FSBL process were as follows: cadmium (69 to 75%), copper (68 to 70%), manganese (72 to 73%), zinc (65 to 66%), and lead (16%). The FSBL process was also found to be effective in removing both fecal and total coliforms (abatement > 5 to 6 log units). The nutrients content (nitrogen, phosphorus, and magnesium) were also preserved in decontaminated sludge.