Francesco Ferella

Study on the influence of various factors in the hydrometallurgical processing of waste printed circuit boards for copper and gold recovery

The present lab-scale experimental study presents the process of leaching waste printed circuit boards (WPCBs) in order to recover gold by thioureation. Preliminary tests have shown that copper adversely affects gold extraction; therefore an oxidative leaching pre-treatment was performed in order to remove base metals. The effects of sulfuric acid concentration, hydrogen peroxide volume and temperature on the metal extraction yield were studied by analysis of variance (ANOVA). The highest copper extraction yields were 76.12% for sample A and 18.29% for sample D, after leaching with 2M H2SO4, 20 ml of 30% H2O2 at 30°C for 3h. In order to improve Cu removal, a second leaching was performed only on sample A, resulting in a Cu extraction yield of 90%. Other experiments have shown the negative effect of the stirring rate on copper dissolution. The conditions used for the process of gold extraction by thiourea were: 20 g/L thiourea, 6g/L ferric ion, 10 g/L sulfuric acid, 600 rpm stirring rate. To study the influence of temperature and particle size, this process was tested on pins manually removed from computer central processing units (CPUs) and on waste CPU for 3½ h. A gold extraction yield of 69% was obtained after 75% of Cu was removed by a double oxidative leaching treatment of WPCBs with particle sizes smaller than 2 mm.

Treatment of exhaust fluorescent lamps to recover yttrium: Experimental and process analyses

The paper deals with recovery of yttrium from fluorescent powder coming from dismantling of spent fluorescent tubes. Metals are leached by using different acids (nitric, hydrochloric and sulphuric) and ammonia in different leaching tests. These tests show that ammonia is not suitable to recover yttrium, whereas HNO(3) produces toxic vapours. A full factorial design is carried out with HCl and H(2)SO(4) to evaluate the influence of operating factors. HCl and H(2)SO(4) leaching systems give similar results in terms of yttrium extraction yield, but the last one allows to reduce calcium extraction with subsequent advantage during recovery of yttrium compounds in the downstream. The greatest extraction of yttrium is obtained by 20% w/v S/L ratio, 4N H(2)SO(4) concentration and 90°C. Yttrium and calcium yields are nearly 85% and 5%, respectively. The analysis of variance shows that acid concentration alone and interaction between acid and pulp density have a significant positive effect on yttrium solubilization for both HCl and H(2)SO(4) medium. Two models are empirically developed to estimate yttrium and calcium concentration during leaching. Precipitation tests demonstrate that at least the stoichiometric amount of oxalic acid is necessary to recover yttrium efficiently and a pure yttrium oxalate n-hydrate can be produced (99% grade). The process is economically feasible if other components of the fluorescent lamps (glass, ferrous and non-ferrous scraps) are recovered after the equipment dismantling and valorized, besides the cost that is usually paid to recycling companies for collection, treatment or final disposal of such fluorescent powders.

Metal recovery from spent refinery catalysts by means of biotechnological strategies.

A bioleaching study aimed at recovering metals from hazardous spent hydroprocessing catalysts was carried out. The exhaust catalyst was rich in nickel (4.5 mg/g), vanadium (9.4 mg/g) and molybdenum (4.4 mg/g). Involved microorganisms were iron/sulphur oxidizing bacteria. Investigated factors were elemental sulphur addition, ferrous iron addition and actions contrasting a possible metal toxicity (either adding powdered activated charcoal or simulating a cross current process by means of periodical filtration). Ferrous iron resulted to be essential for metal extraction: nickel and vanadium extraction yields were 83% and 90%, respectively, while about 50% with no iron. The observed values for molybdenum extraction yields were not as high as Ni and V ones (the highest values were around 30-40%). The investigated actions aimed at contrasting a possible metal toxicity resulted not to be effective; in contrast, sequential filtration of the liquor leach had a significant negative effect on metals extraction. Nickel and vanadium dissolution kinetics resulted to be significantly faster than molybdenum dissolution ones. Furthermore, a simple first order kinetic model was successfully fitted to experimental data. All the observed results supported the important role of the indirect mechanism in bioleaching of LC-Finer catalysts.

A review of metal recovery from spent petroleum catalysts and ash

With the increase in environmental awareness, the disposal of any form of hazardous waste has become a great concern for the industrial sector. Spent catalysts contribute to a significant amount of the solid waste generated by the petrochemical and petroleum refining industry. Hydro-cracking and hydrodesulfurization (HDS) catalysts are extensively used in the petroleum refining and petrochemical industries. The catalysts used in the refining processes lose their effectiveness over time. When the activity of catalysts decline below the acceptable level, they are usually regenerated and reused but regeneration is not possible every time. Recycling of some industrial waste containing base metals (such as V, Ni, Co, Mo) is estimated as an economical opportunity in the exploitation of these wastes. Alkali roasted catalysts can be leached in water to get the Mo and V in solution (in which temperature plays an important role during leaching). Several techniques are possible to separate the different metals, among those selective precipitation and solvent extraction are the most used. Pyrometallurgical treatment and bio-hydrometallurgical leaching were also proposed in the scientific literature but up to now they did not have any industrial application. An overview on patented and commercial processes was also presented.

Recovery of yttrium from cathode ray tubes and lamps’ fluorescent powders: experimental results and economic simulation

In this paper, yttrium recovery from fluorescent powder of lamps and cathode ray tubes (CRTs) is described. The process for treating these materials includes the following: (a) acid leaching, (b) purification of the leach liquors using sodium hydroxide and sodium sulfide, (c) precipitation of yttrium using oxalic acid, and (d) calcinations of oxalates for production of yttrium oxides. Experimental results have shown that process conditions necessary to purify the solutions and recover yttrium strongly depend on composition of the leach liquor, in other words, whether the powder comes from treatment of CRTs or lamp. In the optimal experimental conditions, the recoveries of yttrium oxide are about 95%, 55%, and 65% for CRT, lamps, and CRT/lamp mixture (called MIX) powders, respectively. The lower yields obtained during treatments of MIX and lamp powders are probably due to the co-precipitation of yttrium together with other metals contained in the lamps powder only. Yttrium loss can be reduced to minimum changing the experimental conditions with respect to the case of the CRT process. In any case, the purity of final products from CRT, lamps, and MIX is greater than 95%. Moreover, the possibility to treat simultaneously both CRT and lamp powders is very important and interesting from an industrial point of view since it could be possible to run a single plant treating fluorescent powder coming from two different electronic wastes.

Recovery of yttrium from fluorescent powder of cathode ray tube, CRT: Zn removal by sulphide precipitation

This work is focused on the recovery of yttrium and zinc from fluorescent powder of cathode ray tube (CRT). Metals are extracted by sulphuric acid in the presence of hydrogen peroxide. Leaching tests are carried out according to a 2(2) full factorial plan and the highest extraction yields for yttrium and zinc equal to 100% are observed under the following conditions: 3M of sulphuric acid, 10% v/v of H2O2 concentrated solution at 30% v/v, 10% w/w pulp density, 70°C and 3h of reaction. Two series of precipitation tests for zinc are carried out: a 2(2) full factorial design and a completely randomized factorial design. In these series the factors investigated are pH of solution during the precipitation and the amount of sodium sulphide added to precipitate zinc sulphide. The data of these tests are used to describe two empirical mathematical models for zinc and yttrium precipitation yields by regression analysis. The highest precipitation yields for zinc are obtained under the following conditions: pH equal to 2-2.5% and 10-12%v/v of Na2S concentrated solution at 10%w/v. In these conditions the coprecipitation of yttrium is of 15-20%. Finally further yttrium precipitation experiments by oxalic acid on the residual solutions, after removing of zinc, show that yttrium could be recovered and calcined to obtain the final product as yttrium oxide. The achieved results allow to propose a CRT recycling process based on leaching of fluorescent powder from cathode ray tube and recovery of yttrium oxide after removing of zinc by precipitation. The final recovery of yttrium is 75-80%.

Separation and recovery of glass, plastic and indium from spent LCD panels

The present paper deals with physico-mechanical pre-treatments for dismantling of spent liquid crystal displays (LCDs) and further recovery of valuable fractions like plastic, glass and indium. After a wide experimental campaign, two processes were designed, tested and optimized. In the wet process, 20%, 15% and 40% by weight of the feeding panels are recovered as plastic, glass and indium concentrate, respectively. Instead, in the dry process, only two fractions were separated: around 11% and 85% by weight are recovered as plastic and glass/indium mixture. Indium, that concentrated in the -212μm fraction, was completely dissolved by sulphuric acid leaching (0.75molL-1 H2SO4 solution, 80°C, 10%vol H2O2, pulp density 10%wt/vol, leaching time 3h). 100% of indium can be extracted from the pregnant solution with 5%wt/vol Amberlite™ resin, at room temperature and pH 3 in 24h. Indium was thus re-extracted from the resin by means of a 2molL-1 H2SO4 solution, at room temperature and S/L of 40%wt/vol.

Extraction of Zinc and Manganese from Alkaline and Zinc-Carbon Spent Batteries by Citric-Sulphuric Acid Solution

The paper is focused on the recovery of zinc and manganese from alkaline and zinc-carbon spent batteries. Metals are extracted by sulphuric acid leaching in the presence of citric acid as reducing agent. Leaching tests are carried out according to a full factorial design, and empirical equations for Mn and Zn extraction yields are determined from experimental data as a function of pulp density, sulphuric acid concentration, temperature, and citric acid concentration. The highest values experimentally observed for extraction yields were 97% of manganese and 100% of zinc, under the following operating conditions: temperature , pulp density 20%, sulphuric acid concentration 1.8 M, and citric acid 40 g . A second series of leaching tests is also performed to derive other empirical models to predict zinc and manganese extraction. Precipitation tests, aimed both at investigating precipitation of zinc during leaching and at evaluating recovery options of zinc and manganese, show that a quantitative precipitation of zinc can be reached but a coprecipitation of nearly 30% of manganese also takes place. The achieved results allow to propose a battery recycling process based on a countercurrent reducing leaching by citric acid in sulphuric solution.

Bioassessment of a combined chemical-biological treatment for synthetic acid mine drainage

In this work, ecotoxicological characteristics of synthetic samples of acid mine drainage (AMD) before and after a combined chemical-biological treatment were investigated by using Lepidium sativum and Daphnia magna. AMD treatment was performed in a two-column apparatus consisting of chemical precipitation by limestone and biological refinement by sulphate reducing bacteria. Synthetic samples of AMD before treatment were toxic for both L. sativum (germination index, G, lower than 10%) and D. magna (100% immobility) due to acid pH and presence of copper and zinc. Chemical treatment (raising pH to 5-6 and eliminating copper) generated effluents with reduced toxicity for L. sativum (G=33%), while 100% immobility was still observed for D. magna. Dynamic trends of toxicity for the first and fifth outputs of the biological column denoted a gradual improvement leading to hormesis for Lepidium (after the initial release of organic excess), while a constant residual toxicity remained for Daphnia (probably due to H(2)S produced by sulphate reducing bacteria).

Reducing acid leaching of manganiferous ore: Effect of the iron removal operation on solid waste disposal

The process of reducing acid leaching of manganiferous ore is aimed at the extraction of manganese from low grade manganese ores. This work is focused on the iron removal operation. The following items have been considered in order to investigate the effect of the main operating conditions on solid waste disposal and on the process costs: (i) type and quantity of the base agent used for iron precipitation, (ii) effective need of leaching waste separation prior to the iron removal operation, (iii) presence of a second leaching stage with the roasted ore, which might also act as a preliminary iron removal step, and (iv) effect of tailings washing on the solid waste classification. Different base compounds have been tested, including CaO, CaCO3, NaOH, and Na2CO3. The latter gave the best results concerning both the precipitation process kinetics and the reagent consumption. The filtration of the liquor leach prior to iron removal was not necessary, implying significant savings in capital costs. A reduction of chemical consumption and an increase of manganese concentration in the solution were obtained by introducing secondary leaching tests with the previously roasted ore; this additional step was introduced without a significant decrease of global manganese extraction yield. Finally, toxicity characteristic leaching procedure (TCLP) tests carried out on the leaching solid waste showed: (i) a reduction of arsenic mobility in the presence of iron precipitates, and (ii) the need for a washing step in order to produce a waste that is classifiable as not dangerous, taking into consideration the existing Environmental National Laws.