Vicenç Martí

MODIFICATION AND PREPARATION OF POLYMERIC ADSORBENTS FOR PRECIOUS-METAL EXTRACTION IN HYDROMETALLURGICAL PROCESSES

Abstract This paper describes the efforts made to develop polymeric adsorbents that could be applied to the recovery of precious metals (Au, Pt, Pd and Rh) from cyanide leaching solutions. The polymeric adsorbents prepared should fit they following criteria: be compatible with the nature of the leaching solutions concerned; have good selectivity patterns against the other metal cyanides; have good elution properties and be compatible on integrated systems of leaching and extraction (resin-in-pulp (RIP) and resin-in-leach (RIL)). Knowledge of the chemical speciation of the target metals in the leaching solutions to be treated and the nature and structure of the metal complex to be extracted is very important in understanding the metal-extraction reactions and selectivity factors. As selectivity patterns are greatly influenced by the polymer structure, ionic density and hydrophilic/hydrophobic nature of the polymeric supports, the definition of the structure and functionality of the polymeric supports has been based on the chemical speciation as one of the more effective options fbr polymer support selection. Two methods have been used in selecting polymeric adsorbents: commercial ion-exchange resins and ion-exchange impregnated resins prepared by physical immobilisation of selective and specific reagents used, in solvent extraction onto high surface polymeric materials. Both types of material were evaluated in two applications: extraction and recovery of gold cyanide from leaching liquors and recovery of Pt, Pd and Rh from leaching solutions obtained on cyanidation steps of automobile catalytic converters. The introduction of both polymeric materials is directed towards the selective recovery of gold and precious metals (Pt, Pd, Rh) as an alternative to defined processes based on adsorption steps by activated carbon and/or precipitation by thermal processes.

Capillary electrophoretic determination of cyanide leaching solutions from automobile catalytic converters

A capillary electrophoresis (CE) method to determine metal-cyano complexes from leaching solutions of automobile catalytic converters has been developed. The separation and detection conditions have been optimized and analysis times up to 20 min and metal detection limits in the ppb range have been obtained. The CE analysis of leaching solutions from different converters allowed the determination of Fe(II)-, Cu(I)-, Ni(II)-, Pd(II)- and Pt(II)-cyano complexes and NO - 3 . On the other hand, adsorption onto activated carbon is used as a concentration process for precious metal-cyano complexes and as a process of pollutant removal. The adsorption kinetics of the compounds of interest have been studied by means of the developed CE method. The results obtained by CE have been compared with inductively coupled plasma in order to validate this newly developed method.

Denitrification in presence of acetate and glucose for bioremediation of nitrate‐contaminated groundwater

With the current increasing interest in aquifer denitrification, recent attention has been given to cost‐effective in‐situ treatments such as Enhanced In‐Situ Biological Denitrification (EISBD), which intends to stimulate the indigenous bacterial activity by injecting an external organic substrate and/or nutrients to the aquifer matrix. Within this context, laboratory batch assays have been conducted to develop a strategy for in‐situ denitrification of a nitrate‐contaminated aquifer in Argentona, Catalonia (Spain). The assays were run under aerobic and anaerobic conditions at a temperature of 17°C to better simulate the conditions of the aquifer. Acetate and glucose were added to assess their potential to promote heterotrophic denitrifying bacteria activity. Overall, the results revealed that indigenous micro‐organisms had the potential of reducing nitrate under appropriate conditions. Nitrate removal was complete and faster under anaerobic conditions, though high nitrate removals were also attained under initial aerobic conditions when a readily organic compound was amended at a sufficient dosage. The results also revealed that a significant amount of the available organic carbon was consumed by processes other than denitrification, namely aerobic oxidation and other microbial oxidation processes. To sum up, the results of this study demonstrated that addition of organic compounds into the groundwater is a promising method for in‐situ bioremediation of nitrate in the Argentona aquifer. This approach could potentially be applied to a number of situations in which nitrate concentration is elevated and where indigenous micro‐organisms with potential to reduce nitrate are present within the aquifer material.

Sorption of Antimony (V) onto Synthetic Goethite in Carbonate Medium

Abstract The sorption kinetics of antimony(V) on synthetic goethite is very fast compared to the sorption of other metals on goethite (e.g. arsenic and selenium) and depends on temperature, with an activation energy of 49±9 kJ · mol−1 in the temperature range 15–35°C. Sorption isotherms have been developed at different temperatures and ionic strength values. The results have been modelled using a Langmuir isotherm and there is not a considerable influence of neither the temperature in the range studied (15°C–35°C), nor the ionic strength (between 0.001 and 0.01 mol · dm−3). Sorption is very high at pH values lower than 8, at more alkaline pH, the sorption decreases with pH, as expected considering the Antimony(V) predominating complex in solution, Sb(OH)6 −. Triple‐layer model successfully describes the data obtained by assuming a bidentate edge‐sharing surface complex of antimonate on the surface of goethite.

Determination of metal cyanide complexes in gold processing solutions by capillary electrophoresis

Abstract A capillary electrophoresis method to determine metal cyanide complexes and sulphur compounds in gold processing solutions using direct UV absorbance detection has been developed. The method is based on the use of electroosmotic flow modifiers, such as C 17 H 38 NBr, to control the separation and in the on-column concentration of the sample by using the stacking effect to increase the sensitivity. By optimizing the analytical conditions, analysis times of less than 15 min and detection limits of metals in the mid-ppb range have been obtained with good resolution. The quantitation and determination of the metal cyanide complexes Au(CN) 2 − , Ag(CN) 2 − , Cu(CN) 3 2− , Ni(CN) 4 2− and Fe(CN) 6 4− , HS − and SCN − , present in samples from the leaching of a gold mineral (Minas Gerais, Brazil) and a gold sand (Itenez, Bolivia) by using a sodium cyanide (NaCN) solution (1000 ppm and pH 10.5 adjusted with CaO, as in real processes), has been achieved. Finally, the evolution of the formation within the time of gold cyanide complexes under leaching conditions has been studied by using the analytical method proposed.

Life cycle and human health risk assessments as tools for decision making in the design and implementation of nanofiltration in drinking water treatment plants

A combined methodology using life cycle assessment (LCA) and human health risk assessment (HHR) is proposed in order to select the percentage of water in drinking water treatment plants (DWTP) that should be nanofiltered (NF). The methodological approach presented here takes into account environmental and social benefit criteria evaluating the implementation of new processes into conventional ones. The inclusion of NF process improves drinking water quality, reduces HHR but, in turn, increases environmental impacts as a result of energy and material demand. Results from this study lead to balance the increase of the impact in various environmental categories with the reduction in human health risk as a consequence of the respective drinking water production and consumption. From an environmental point of view, the inclusion of NF and recommended pretreatments to produce 43% of the final drinking water means that the environmental impact is nearly doubled in comparison with conventional plant in impact categories severely related with electricity production, like climate change. On the other hand, the carcinogenic risk (HHR) associated to trihalomethane formation potential (THMFP) decreases with the increase in NF percentage use. Results show a reduction of one order of magnitude for the carcinogenic risk index when 100% of drinking water is produced by NF.

Effects of enhanced denitrification on hydrodynamics and microbial community structure in a soil column system

Enhanced heterotrophic denitrification by adding glucose was investigated by means of a soil column experiment which simulated the groundwater flow. The carbon-to-nitrogen ratio was the main factor determining denitrification potential under experimental conditions. The influence of stimulated denitrification on the autochthonous microbial community was investigated by quantitative PCR (qPCR), and denaturing gradient gel electrophoresis (DGGE). The qPCR detection of the nosZ genes encoding nitrous oxide reductase, and the comparison of the abundances of 16S rRNA genes revealed that the addition of glucose enhanced denitrification leading to an increase in both the total eubacteria and, in particular, in the ratio of denitrifying bacteria, which represented the 21% of the total native eubacteria on the basis of nosZ/16S rRNA gene ratio. Microbial community profiling by DGGE indicated that ribotypes closely related to the genera Acidovorax and Hydrogenophaga (Comamonadaceae family) became enriched in the soil column. The effects of biomass occurrence in the column system on soil hydrodynamics, assessed by tracer studies, revealed a reduction of porosity and a significant increase of dispersivity that could be caused by the appearance of new functional microbial biomass in the aquifer material under enhanced denitrifying conditions. The importance of investigating the microbial growth in relation to the hydrodynamic effects, during enhanced denitrification, has been revealed in the column system experiments associated with the bioremediation. Combining microbial characterisation and hydrodynamic data in a soil column system permits us to gain an insight to the limiting factors of different stimulation strategies that can be applied in the field.

Determination of the equilibrium formation constants of two U(VI)–peroxide complexes at alkaline pH

The formation of uranyl-peroxide complexes was studied at alkaline media by using UV-Visible spectrophotometry and the STAR code. Two different complexes were found at a H(2)O(2)/U(VI) ratio lower than 2. A graphical method was used in order to obtain the formation constants of such complexes and the STAR program was used to refine the formation constants values because of its capacity to treat multiwavelength absorbance data and refining equilibrium constants. The values obtained for the two complexes identified were: UO(2)(2+) + H(2)O(2) + 4OH(-) <−> UO(2)(O(2))(OH)(2)(2-) + 2H(2)O: log β°(1,1,4) = 28.1 ± 0.1 (1). UO(2)(2+) + 2H(2)O(2) + 6OH(-) <−> UO(2)(O(2))(2)(OH)(2)(4-) + 4H(2)O: log β°(1,2,6) = 36.8 ± 0.2 (2). At hydrogen peroxide concentrations higher than 10(-5) mol dm(-3), and in the absence of carbonate, the UO(2)(O(2))(2)(OH)(2)(4-) complex is predominant in solution, indicating the significant peroxide affinity of peroxide ions for uranium and the strong complexes of uranium(VI) with peroxide.

Analysis of phenoxyalkyl acid herbicides and chlorophenols by capillary zone electrophoresis

Abstract A capillary zone electrophoresis system (CZE) with on-line UV detection was used for the determination of two phenoxyalkyl acid herbicides (2,4-D and 2,4,5-TP) and two chlorophenols (2,4-dichlorophenol and 2,4,5-trichlorophenol). Under an applied voltage of 23 kV, all compounds migrated towards the cathode within 10 min. Phosphate buffer was used and the separation of different species was achieved by combining electrophoretic and electro-osmotic effects. The coefficient of electro-osmotic flow and the electrophoretic mobilities of individual compounds were calculated. A linear relationship between peak area and sample amount was obtained in the range of 4–56 pg for 2,4-D, 2,4,5-TP and 2,4,-dichlorophenol and of 10–46 pg for 2,4,5-trichlorophenol. The detection limit was lower than 6 pg. The coefficients of variation of peak area and retention time were 3.4–6.1% and 0.2%, respectively.

Assessment of the water chemical quality improvement based on human health risk indexes: Application to a drinking water treatment plant incorporating membrane technologies.

A methodology has been developed in order to evaluate the potential risk of drinking water for the health of the consumers. The methodology used for the assessment considered systemic and carcinogenic effects caused by oral ingestion of water based on the reference data developed by the World Health Organisation (WHO) and the Risk Assessment Information System (RAIS) for chemical contaminants. The exposure includes a hypothetical dose received by drinking this water according to the analysed contaminants. An assessment of the chemical quality improvement of produced water in the Drinking Water Treatment Plant (DWTP) after integration of membrane technologies was performed. Series of concentration values covering up to 261 chemical parameters over 5 years (2008-2012) of raw and treated water in the Sant Joan Despí DWTP, at the lower part of the Llobregat River basin (NE Spain), were used. After the application of the methodology, the resulting global indexes were located below the thresholds except for carcinogenic risk in the output of DWTP, where the index was slightly above the threshold during 2008 and 2009 before the upgrade of the treatment works including membrane technologies was executed. The annual evolution of global indexes showed a reduction in the global values for all situations: HQ systemic index based on RAIS dropped from 0.64 to 0.42 for surface water and from 0.61 to 0.31 for drinking water; the R carcinogenic index based on RAIS was negligible for input water and varied between 4.2×10(-05) and 7.4×10(-06) for drinking water; the W systemic index based on the WHO data varied between 0.41 and 0.16 for surface water and between 0.61 and 0.31 for drinking water. A specific analysis for the indexes associated with trihalomethanes (THMs) showed the same pattern.