J.L. Cortina

Sorption kinetics of polycyclic aromatic hydrocarbons removal using granular activated carbon: Intraparticle diffusion coefficients

Granular activated carbon (GAC) was evaluated as a suitable sorbent for polycyclic aromatic hydrocarbons (PAHs) removal from aqueous solutions. For this purpose, kinetic measurements on the extraction of a family of six PAHs were taken. A morphology study was performed by means of a scanning electron microscopy (SEM) analysis of GAC samples. Analyses of the batch rate data for each PAH were carried out using two kinetic models: the homogenous particle diffusion model (HPDM) and the shell progressive model (SPM). The process was controlled by diffusion rate the solutes (PAHs) that penetrated the reacted layer at PAH concentrations in the range of 0.2-10 mg L(-1). The effective particle diffusion coefficients (D(eff)) derived from the two models were determined from the batch rate data. The Weber and Morris intraparticle diffusion model made a double contribution to the surface and pore diffusivities in the sorption process. The D(eff) values derived from both the HPMD and SPM equations varied from 1.1 x 10(-13) to 6.0 x 10(-14) m(2) s(-1). The simplest model, the pore diffusion model, was applied first for data analysis. The model of the next level of complexity, the surface diffusion model, was applied in order to gain a deeper understanding of the diffusion process. This model is able to explain the data, and the apparent surface diffusivities are in the same order of magnitude as the values for the sorption of functionalized aromatic hydrocarbons (phenols and sulphonates) that are described in the literature.

Phenol removal from aqueous solution by adsorption and ion exchange mechanisms onto polymeric resins

The removal of phenol from aqueous solution was evaluated by using a nonfunctionalized hyper-cross-linked polymer Macronet MN200 and two ion exchange resins, Dowex XZ (strong anion exchange resin) and AuRIX 100 (weak anion exchange). Equilibrium experimental data were fitted to the Langmuir and Freundlich isotherms at different pHs. The Langmuir model describes successfully the phenol removal onto the three resins. The extent of the phenol adsorption was affected by the pH of the solution; thus, the nonfunctionalized resin reported the maximum loading adsorption under acidic conditions, where the molecular phenol form predominates. In contrast both ion exchange resins reported the maximum removal under alkaline conditions where the phenolate may be removed by a combined effect of both adsorption and ion exchange mechanisms. A theoretical model proposed in the literature was used to fit the experimental data and a double contribution was observed from the parameters obtained by the model. Kinetic experiments under different initial phenol concentrations and under the best pH conditions observed in the equilibrium experiments were performed. Two different models were used to define the controlling mechanism of the overall adsorption process: the homogeneous particle diffusion model and the shell progressive model fit the kinetic experimental data and determined the resin phase mechanism as the rate-limiting diffusion for the phenol removal. Resins charged after the kinetic experiments were further eluted by different methods. Desorption of nonfunctionalized resin was achieved by using the solution (50% v/v) of methanol/water with a recovery close to 90%. In the case of the ion exchange resins the desorption process was performed at different pHs and considering the effect of the competitive ion Cl-. The desorption processes were controlled by the ion exchange mechanism for Dowex XZ and AuRIX 100 resins; thus, no significant effect for the addition of Cl- under acidic conditions was observed, while under alkaline conditions the total recovery increased, specially for Dowex XZ resin.

Treatment of acid mine drainage by sulphate-reducing bacteria using permeable reactive barriers: A review from laboratory to full-scale experiments

Acid mine drainage in-situbioremediation has in the last decades drawnthe attention in the field of environmentalbiotechnology. The most recent treatmenttechnique are the permeable reactive barriersusing sulphate-reducing bacteria. This viewdescribes the basis of many of the currentapproaches to use sulphate-reducing bacteria inacid mine drainage treatment, from laboratoryto full-scale realisations, and the limitationsencountered when applied to full scaleapplications.

Removal of cadmium, copper, nickel, cobalt and mercury from water by Apatite II™: Column experiments

Apatite II™, a biogenic hydroxyapatite, was evaluated as a reactive material for heavy metal (Cd, Cu, Co, Ni and Hg) removal in passive treatments. Apatite II™ reacts with acid water by releasing phosphates that increase the pH up to 6.5-7.5, complexing and inducing metals to precipitate as metal phosphates. The evolution of the solution concentration of calcium, phosphate and metals together with SEM-EDS and XRD examinations were used to identify the retention mechanisms. SEM observation shows low-crystalline precipitate layers composed of P, O and M. Only in the case of Hg and Co were small amounts of crystalline phases detected. Solubility data values were used to predict the measured column experiment values and to support the removal process based on the dissolution of hydroxyapatite, the formation of metal-phosphate species in solution and the precipitation of metal phosphate. Cd(5)(PO(4))(3)OH(s), Cu(2)(PO(4))OH(s), Ni(3)(PO(4))(2)(s), Co(3)(PO(4))(2)8H(2)O(s) and Hg(3)(PO(4))(2)(s) are proposed as the possible mineral phases responsible for the removal processes. The results of the column experiments show that Apatite II™ is a suitable filling for permeable reactive barriers.

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.

Presence and biological effects of emerging contaminants in Llobregat River basin: A review

Llobregat River (North-East Spain) is the most important drinking water source for Barcelona and its surrounding area. As one of the only water sources in the area the river water have been overexploited and effluents from more than 30 urban wastewater treatment plants, industries and agriculture runoffs have been discharged into the river. This article reviews the presence of emerging contaminants published during the last decades, emphasizing on the observed effects on ecosystems caused by the contamination. Pesticides, surfactants, estrogens, pharmaceuticals and personal care products and even abuse drugs are the main groups detected in different studies, reporting alterations in species composition, abundance or biomass and endocrine disruption measured by alterations in enzymatic activity or specific protein production. The information available provides an overview of the river status according to the Water Framework Directive.

Modelling of mass transfer in facilitated supported liquid membrane transport of gold(III) using phospholene derivatives as carriers

Abstract An experimental study of gold(III) transport through solid-supported liquid membranes using phospholene derivatives as carriers has been performed using batch experiments. A model is reported describing the transport mechanism which consists of a diffusion process through a feed aqueous diffusion layer, a fast interfacial chemical reaction and a diffusion of HAuCl 4 L and HAuCl 4 L 2 through the membrane. The mathematical equations describing the rate of transport are derived and correlate the membrane permeability coefficient to diffusional and equilibrium parameters as well as the chemical composition of the system, such as extractant concentration in the membrane phase and HCl concentration in the feed phase. The experimental data are explained with the derived equations, and the diffusion resistances to mass transfer are evaluated. The influence in the transport of stirring speed in the feed phase, the nature of the diluent and stripping agent, and the type of polymeric support have been also discussed.

Oxidation by Fenton's reagent combined with biological treatment applied to a creosote-comtaminated soil.

In this study, we investigated the feasibility of using Fenton oxidation to remove sorbed polycyclic aromatic hydrocarbons (PAHs) in aged soil samples with creosote oil from a wood preserving site. The optimal dosage of reagents was determined by a statistical method, the central composite rotatable experimental design. The maximum PAH removal was 80% with a molar ratio of oxidant/catalyst equal to 90:1. In general low molecular weight PAHs (3 rings) were degraded more efficiently than higher molecular weight PAHs (4 and 5 rings). The hydrogen peroxide decomposition kinetic was studied in the presence of KH(2)PO(4) as stabilizer. The kinetic data were fitted to a simple model, the pseudo-first-order which describes the hydrogen peroxide decomposition. The PAH kinetic degradation was also studied, and demonstrated that non-stabilized hydrogen peroxide was consumed in less than 30 min, whilst PAH removal continued for up to 24h. In a second part of the work, a combined chemical and biological treatment of the soil was carried out and shown to be dependent on the pre-oxidation step. Different reagent doses (H(2)O(2):Fe) were used (10, 20, 40, 60:1) in the pre-treatment step. An excess of hydrogen peroxide resulted in a poor biological removal, thus the optimal molar ratio of H(2)O(2):Fe for the combined process was 20:1. The combined treatment resulted in a maximum total PAH removal of 75% with a 30% increase in removal due to the biodegradation step. The sample with highest PAH removal in the pre-oxidation step led to no further increase in removal by biological treatment. This suggests that the more aggressive chemical pre-oxidation does not favour biological treatment. The physico-chemical properties of the pollutants were an important factor in the PAH removal as they influenced chemical, biological and combined treatments.

Analysis of the occurrence and risk assessment of polar pesticides in the Llobregat River Basin (NE Spain)

Contamination of surface waters by pesticides continues to be the focus of concern for water authorities due to the growing evidence of their deleterious effects on aquatic life. In this context, the present work investigates the occurrence of 16 selected pesticides belonging to the classes of triazines, phenylureas, organophosphates, chloroacetanilides and thiocarbamates in surface waters from the Llobregat River (NE Spain) and some of its tributaries (Anoia and Rubí) and assesses their potential impact on the aquatic organisms by applying a recently developed index, the Short-term Pesticide Risk Index for the Surface Water System (PRISW-1), which takes into account the pesticides concentrations and their overall toxicity against three aquatic organisms (algae, Daphnia, and fish). Chemical analysis, performed by means of a fully automated method based on isotope dilution on-line solid phase extraction-liquid chromatography-electrospray-tandem mass spectrometry (on-line SPE-LC-ESI-MS/MS), revealed diuron and diazinon as the most ubiquitous and abundant compounds with levels up to 818 and 132 ng L(-1), respectively. Total pesticide concentrations, which in only 1 out of 66 samples surpassed 500 ng L(-1), were higher in the tributaries than in the river but their contribution in terms of mass-loads to the overall pesticide pollution of the Llobregat River was relatively small. Contamination increased downstream of the river and was clearly influenced by rainfall and hence river flow. Application of the PRISW-1 index indicated that, although pesticides levels fulfilled the European Union Environmental Quality Standards (EQS) for surface waters, the existing pesticide contamination poses a low to high ecotoxicological risk for aquatic organisms, that algae and macro-invertebrates are at higher risk than fish, and that the organophosphates diazinon and malathion and the phenylurea diuron are the major contributors to the overall toxicity and therefore the most problematic compounds.

Kinetics of goldcyanide extraction using ion-exchange resins containing piperazine functionality

Abstract The search for suitable resins for goldcyanide recovery from cyanide solutions prompted the synthesis of resins incorporating new functionalities that solve many of the existing problems. A new type of ion-exchange resin (PS-PIP) incorporating a piperazine group, linked onto a styrene–divinylbenzene macroporous network, was developed for goldcyanide solutions. Kinetics measurements were made on the extraction of goldcyanide (Au(CN) 2 − ) with the ion-exchange resin (PS-PIP). The extraction process is accompanied by fast ion-exchange reaction and is characterised by a sharp moving boundary between the reacted shell and the shrinking unreacted core within the resin. Analyses of the respective rate data in accordance with two theoretical models used to explain the metal extraction kinetics showed that the process is controlled by the rate of diffusion of the ions penetrating the reacted layer at goldcyanide concentrations in the range 10–40 mg l −1 and controlled by the rate of diffusion of the ions across the liquid film surrounding the resin particle at goldcyanide concentrations lower than −1 . Particle diffusion coefficients and mass transfer constants across the liquid film were determined from the graphical representation of the proposed models.