Núria Fiol

Arsenic removal by a waste metal (hydr)oxide entrapped into calcium alginate beads.

In this work, a solid waste material from an electroplating industrial plant has been investigated for As(III) and As(V) sorption. This sorbent, a mixture of mainly Fe(III) and Ni(II) (hydr)oxides, has been used both in its native form and entrapped in calcium alginate. The effect of sorbent concentration in the gel bead, solution pH, contact time and As(III) and As(V) concentration on sorption has been studied. Furthermore the effect of the gel matrix has been investigated. A 10% (w/v) of (hydr)oxide in the gel beads was found to provide both spherical beads shape and good sorption performance. Solution pH was found to exert a stronger influence in As(V) than in As(III) sorption. The optimum pH range resulted to be within 5-10 for As(III) and within 6-9 for As(V). Taking into account these results, pH 8 was chosen for further sorption experiments. Equilibrium was reached after 48 h contact time for the studied systems. Kinetics data of both As(III) and As(V) onto native (hydr)oxide (O) and entrapped in calcium alginate beads (10% O-CA) were successfully modelled according to pseudo-first and pseudo-second order equations. Sorption equilibrium data were evaluated by the Langmuir isotherm model and the maximum capacity q(max) were 77.4 and 126.5 mg g(-1) for As(III) on O and 10% O-CA, and 26.8 and 41.6 mg g(-1) for As(V) on O and 10% O-CA, respectively. The entrapment of the (hydr)oxide in a calcium alginate gel matrix improved the As(III) and As(V) sorption by 60%.

Chromium (VI) uptake by grape stalks wastes encapsulated in calcium alginate beads: equilibrium and kinetics studies

Abstract The removal of hexavalent chromium from aqueous solution using grape stalks wastes encapsulated in calcium alginate (GS–CA) beads was investigated. Cr(VI) sorption kinetics were evaluated as a function of chromium initial concentration and grape stalks (GS) content in the calcium alginate (CA) beads. The process follows pseudo second-order kinetics. Transport properties of hexavalent chromium on GS–CA beads was characterised by calculating chromium diffusion coefficient using the Linear Absorption Model (LAM). Langmuir isotherms, at pH 3.0 were used to describe sorption equilibrium data as a function of GS percentage in the CAbeads. Maximum uptake obtained was 86.42 mmol of Cr(VI) per L of wet sorbent volume. Results indicated that both kinetic and equilibrium models describe adequately the adsorption process.

Re‐use of Exhausted Ground Coffee Waste for Cr(VI) Sorption

Abstract Exhausted ground coffee waste has been investigated as metal biosorbent for Cr(VI) from aqueous solution. Maximum metal sorption was found to occur at initial pH 3.0. Kinetic studies revealed that the initial uptake was quite rapid; nevertheless, it took five days to reach equilibrium. The value of the Langmuir maximum uptake was found to be 10.2 mg Cr(VI)/g waste. The sorbent is able to reduce hexavalent chromium to its trivalent form. A solution of 1 M NaOH was the most effective desorption agent and after 24 hours contact 42% of total chromium was desorbed in both hexavalent and trivalent oxidation states.

Copper(II) and nickel(II) uptake from aqueous solutions by cork wastes: a NMR and potentiometric study

Due to the increasing interest in the use of biomasses from agriculture as removing agents for heavy metals in waste effluents, we present here a joint potentiometric and 13C MAS and cross polarization-magic angle spinning NMR (CP-MAS NMR) study on cork interaction with Cu(II) and Ni(II). Through potentiometry we were able to distinguish two kind of interactions, a stronger one which involves protonated sites on cork and a second that allows hydroxide precipitation of the bound metal ion into the cork structure. NMR signal analysis suggests a specific metal complexation on the carbohydrate moieties of polymeric cork matrix. The 13C MAS NMR suggests that the dynamics in the MHz range and the overall arrangement of polymeric matrix is not affected by metal binding; and the spin relaxation times T1ρ(1H) and T1ρ(13C) show that no significant difference of relaxation processes in the KHz range is introduced by metal coordination.

Modeling of kinetics of Cr(VI) sorption onto grape stalk waste in a stirred batch reactor.

Recently, Cr(VI) removal by grape stalks has been postulated to follow two mechanisms, adsorption and reduction to trivalent chromium. Nevertheless, the rate at which both processes take place and the possible simultaneity of both processes has not been investigated. In this work, kinetics of Cr(VI) sorption onto grape stalk waste has been studied. Experiments were carried out at different temperatures but at a constant pH (3+/-0.1) in a stirred batch reactor. Results showed that three steps take place in the process of Cr(VI) sorption onto grape stalk waste: Cr(VI) sorption, Cr(VI) reduction to Cr(III) and the adsorption of the formed Cr(III). Taking into account the evidences above mentioned, a model has been developed to predict Cr(VI) sorption on grape stalks on the basis of (i) irreversible reduction of Cr(VI) to Cr(III) reaction, whose reaction rate is assumed to be proportional to the Cr(VI) concentration in solution and (ii) adsorption and desorption of Cr(VI) and formed Cr(III) assuming that all the processes follow Langmuir type kinetics. The proposed model fits successfully the kinetic data obtained at different temperatures and describes the kinetics profile of total, hexavalent and trivalent chromium. The proposed model would be helpful for researchers in the field of Cr(VI) biosorption to design and predict the performance of sorption processes.

Grape Stalks Waste as Low Cost Biosorbents: An Alternative for Metal Removal from Aqueous Solutions

Abstract Grape stalks waste generated in the wine production process has been investigated as metal sorbent for Pb(II), Ni(II), Cu(II), and Cd(II) from aqueous solutions. Kinetic studies revealed that the initial uptake was rapid and equilibrium was established in one hour. The results obtained from batch experiments at initial pH 6.0±0.5 were described by the Langmuir isotherm. The highest value of the Langmuir maximum uptake, (q max ), was found for cadmium (0.248 mmol g−1) followed by lead (0.241 mmol g−1), nickel (0.181 mmol g−1), and copper (0.159 mmol g−1). Column experiments were also performed at a constant metal concentration of around 0.250 mmol dm−3 at pH 6.0±0.5 and the results were modelled by means of the reactive transport code RETRASO (REactive TRAnsport of SOlutes) applying a Langmuir sorption mechanism as well. The values obtained from both experimental approaches are found to coincide fairly well. The Langmuir constants (L mol−1) determined are: Copper (1.5 · 103 and 1.0 · 104), Nickel (1.4 · 103 and 2.5 · 103), Lead (8.3 · 104 and 3.5 · 103), and Cadmium (7.0 · 103 and 4.5 · 103), where values in parenthesis correspond to the batch and column determinations, respectively.

Grape Stalks Wastes Encapsulated in Calcium Alginate Beads for Cr(VI) Removal from Aqueous Solutions

Abstract In this study, a low‐cost effective adsorbent based on grape stalks encapsulated in calcium alginate beads was investigated as a possible sorbent for the removal of Cr(VI) from aqueous solution. The present paper deals with the procedure for the preparation of calcium alginate beads and the encapsulation of grape stalks powder into calcium alginate beads, the characterization of these beads and the study of their behavior on Cr(VI) adsorption from aqueous solutions. The influence of grape stalks powder concentration in the calcium alginate beads, metal solution pH, sodium chloride, and metal concentration on metal removal has been studied. Uptake showed a pH‐dependent profile. Maximum Cr(VI) sorption was achieved at pH 3.0. High NaCl concentrations significantly reduce the mechanical resistance of the beads, however, this does not have a significant effect on metal removal. Langmuir and Freundlich isotherms were used to describe sorption equilibrium data. The experimental data were fitted better by the Langmuir adsorption isotherm. The Langmuir adsorption capacity for calcium alginate beads containing 2% (w/v) grape stalks powder was found to be 71.98 10−3 mg/bead (≈225 mg Cr(VI)/g grape stalks).

Adsorption on Activated Carbon from Olive Stones: Kinetics and Equilibrium of Phenol Removal from Aqueous Solution

Activated carbon is prepared with chemical activation of olive stones, by using H3PO4. Batch adsorption of phenol from aqueous solution was investigated. The adsorptive properties were studied in terms of pH, equilibrium time, initial concentration (C0: 25-300 mg/L) and particle sizes (0.125-1.6mm) effects. The experimental kinetic data fitted well the pseudo second order model and the equilibrium isotherm data the Langmuir model. The results indicate that chemical olive stones activated carbon is suitable to be used as an adsorbent material for adsorption of phenol from aqueous solution.

Single and binary adsorption of some heavy metal ions from aqueous solutions by activated carbon derived from olive stones

ABSTRACTIn the present work, activated carbon synthesized from olive stones was used for heavy metal ions (Cu(II), Ni(II), and Pb(II)) removal in single and binary aqueous solutions. The effect of initial solution pH was studied. The equilibrium isotherms for single systems were evaluated in terms of maximum adsorption capacity and adsorption affinity by the application of Langmuir model. Metal ions adsorption increases in the following order: Pb(II) > Ni(II) ≥ Cu(II). The examination of binary adsorption systems: Cu–Ni and Cu–Pb shows that the affinity of copper on the activated carbon surface was strongly dependent on initial concentration of nickel and lead. Copper adsorption was found to increase in the presence of nickel and to decrease in the presence of lead.

Extraction of espresso coffee by using gradient of temperature. Effect on physicochemical and sensorial characteristics of espresso.

Espresso extraction is generally carried out at a fixed temperature within the range 85-95°C. In this work the extraction of the espressos was made in a new generation coffee machine that enables temperature profiling of the brewing water. The effect of using gradient of temperature to brew espressos on physicochemical and sensorial characteristics of the beverage has been investigated. Three different extraction temperature profiles were tested: updrawn gradient (88-93°C), downdrawn gradient (93-88°C) and fixed temperature (90°C). The coffee species investigated were Robusta, Arabica natural and Washed Arabica. Results proved that the use of gradient temperature for brewing espressos allows increasing or decreasing the extraction of some chemical compounds from coffee grounds. Moreover an appropriate gradient of temperature can highlight or hide some sensorial attributes. In conclusion, the possibility of programming gradient of temperature in the coffee machines recently introduced in the market opens new expectations in the field of espresso brewing.