A. Florido

Modelling of the Ni(II) removal from aqueous solutions onto grape stalk wastes in fixed-bed column.

Grape stalk wastes generated in the wine production process were used for the removal of nickel (II) from aqueous solution. The experimental breakthrough curves were obtained in fixed-bed columns. Experiments we carry out in order to evaluate the influence of inlet metal concentration (30 and 70 mg L(-1)) and the regeneration process in a double sorption cycle. The CXTFIT code was used to fit the experimental data and to determine the transport and sorption parameters of the convective-dispersive equation (CDE) and the two-site deterministic non-equilibrium (TSM/CDE) model by adjusting the models to the experimental breakthrough curves (BTC). The results showed that bed capacity as well as transport and sorption parameters were affected by the initial metal concentration, at the highest Ni(II) concentration the grape stalks column saturated quickly leading to earlier breakthrough. The sorption capacity of the sorbent was slightly reduced in a double sorption cycle, while the recovery of the metal in the desorption step was ranging between 80% and 85% in both cycles.

Iodide-selective electrodes based on the silver(I) complex of a novel N-thiocarbamoylimine-dithioether derivative

Abstract Poly(vinyl chloride) membrane ion-selective electrodes (ISEs) based on the silver complex of a novel thiocarbamoylimine dithioether synthesized in our laboratories as an anion carrier have been developed. An anti-Hofmeister behaviour was obtained, and electrodes responded preferentially to iodide. The response of the electrodes was Nernstian for iodide and sub Nernstian for thiocyanate and bromide ions. Detection limits around 7.5 × 10 −9 M and response times of about 10s were obtained for the iodide response of these electrodes. The use of metal-complexes as ionophores in the development of anion-selective electrodes and a comparison among different iodide-responsive membranes are discussed.

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.

Potentiometric electronic tongue-flow injection analysis system for the monitoring of heavy metal biosorption processes.

An automated flow injection potentiometric (FIP) system with electronic tongue detection (ET) is used for the monitoring of biosorption processes of heavy metals on vegetable wastes. Grape stalk wastes are used as biosorbent to remove Cu(2+) ions in a fixed-bed column configuration. The ET is formed by a 5-sensor array with Cu(2+) and Ca(2+)-selective electrodes and electrodes with generic response to heavy-metals, plus an artificial neural network response model of the sensors cross-response. The real-time monitoring of both the Cu(2+) and the cation exchanged and released (Ca(2+)) in the effluent solution is performed by using flow-injection potentiometric electronic tongue system. The coupling of the electronic tongue with automation features of the flow-injection system allows us to accurately characterize the Cu(2+) ion-biosorption process, through obtaining its breakthrough curves, and the profile of the Ca(2+) ion release. In parallel, fractions of the extract solution are analysed by spectroscopic techniques in order to validate the results obtained with the reported methodology. The sorption performance of grape stalks is also evaluated by means of well-established sorption models.

Sequential flow-injection determination of cyanide and weak metal—cyanide complexes with flow-through heterogeneous membrane electrodes

Abstract Free cyanide and cyanide present in weak complexes are determined by using two flow- through silver iodide/silver sulphide electrodes with an intervening gas diffusion unit. Under optimal conditions, the linear range is 10 −5 −10 −3 mol dm −3 cyanide, and the relative standard deviations are ca. 2%, with a sampling rate of 20 h −1 . Total cyanide can be determined in the presence of Zn(II), Cu(II) and Cd(II) but results are low with Ni(II), Co(II) or Fe(III) present. Sulphide and thiocyanate must be absent.

Removal of interferences in the spectrophotometric determination of cyanide by dialysis using flow injection analysis

SummaryFlow injection analysis (FIA) has been combined with a dialysis unit in order to study the effect of interferences in the determination of free cyanide in waste water. Two kinds of interferences, metals and inorganic anions, were studied. In all the cases, solutions of constant cyanide concentration containing interferences were introduced in the FIA system and free cyanide was determined after hydrogen cyanide passes the dialysis membrane.Results reveal the advantages of this methodology for Zn(II), Cu(I), Cd(II), Nr4+ and inorganic anions. Fe(III), Co(II), Ni(II) and carbonate show different behaviour under these conditions.

Development of a multiparametric system based on solid-state microsensors for monitoring a nuclear waste repository

Abstract Nuclear waste repositories are being installed in deep excavated rock formations in some places in Europe to isolate and store radioactive waste. Containers with radioactive waste are also protected with barriers made from porous materials such as bentonite. The objective of this work is to study the transport of radioactive compounds thorough bentonite models to obtain a database of the bentonite–water interaction processes. Among the chemical parameters tested in these barriers, the most significant are pH, conductivity and redox potential. For that purpose, solid-state microsensors fabricated with silicon semiconductor technology such as ion sensitive field effect transistors (ISFETs) for measuring pH and interdigitated structures (IDS) for measuring conductivity and redox potential were used. Response characteristics of these sensors were tested in aqueous samples with compositions similar to those present inside a bentonite barrier and results were compared with those obtained with commercial electrodes obtaining a good agreement between commercial and our sensors.

Simultaneous and automated monitoring of the multimetal biosorption processes by potentiometric sensor array and artificial neural network

In this communication, a new methodology for the simultaneous and automated monitoring of biosorption processes of multimetal mixtures of polluting heavy metals on vegetable wastes based on flow-injection potentiometry (FIP) and electronic tongue detection (ET) is presented. A fixed-bed column filled with grape stalks from wine industry wastes is used as the biosorption setup to remove the metal mixtures from the influent solution. The monitoring system consists in a computer controlled-FIP prototype with the ET based on an array of 9 flow-through ion-selective electrodes and electrodes with generic response to divalent ions placed in series, plus an artificial neural network response model. The cross-response to Cu(2+), Cd(2+), Zn(2+), Pb(2+) and Ca(2+) (as target ions) is used, and only when dynamic treatment of the kinetic components of the transient signal is incorporated, a correct operation of the system is achieved. For this purpose, the FIA peaks are transformed via use of Fourier treatment, and selected coefficients are used to feed an artificial neural network response model. Real-time monitoring of different binary (Cu(2+)/ Pb(2+)), (Cu(2+)/ Zn(2+)) and ternary mixtures (Cu(2+)/ Pb(2+)/ Zn(2+)), (Cu(2+)/ Zn(2+)/ Cd(2+)), simultaneous to the release of Ca(2+) in the effluent solution, are achieved satisfactorily using the reported system, obtaining the corresponding breakthrough curves, and showing the ion-exchange mechanism among the different metals. Analytical performance is verified against conventional spectroscopic techniques, with good concordance of the obtained breakthrough curves and modeled adsorption parameters.

Computer controlled-flow injection potentiometric system based on virtual instrumentation for the monitoring of metal-biosorption processes.

A completely automated flow-injection system was developed for the monitoring of biosorption studies of Cu(II) ion on vegetable waste by-products. The system employed flow-through Cu(II)-selective electrodes, of epoxy-resin-CuS/Ag(2)S heterogeneous crystalline type, and computer controlled pumps and valves for the flow operation. Computer automation was done through a specially devised virtual instrument, which commanded and periodically calibrated the system, allowing for the monitoring of Cu(II) ions between 0.6 and 6530 mg L(-1) at a typical frequency of 15 h(-1). Grape stalk wastes were used as biosorbent to remove Cu(II) ions in a fixed-bed column with a sorption capacity of 5.46 mg g(-1), obtained by the developed flow system, while the reference determination performed by FAAS technique supplied a comparable value of 5.41 mg g(-1).

Electronic Tongue‐FIA system for the Monitoring of Heavy Metal Biosorption Processes

An automated flow injection potentiometric (FIP) system with electronic tongue detection (ET) was used for the monitoring of biosorption processes of heavy metals on waste biomaterial. Grape stalk wastes were used as biosorbent to remove Cu2+ ions in a fixed‐bed column setup. For the monitoring, the used ET employed a sensor array formed by Cu2+ and Ca2+ selective electrodes and two generic heavy‐metal electrodes. The subsequent cross‐response obtained was processed by a multilayer artificial neural network (ANN) model in order to resolve the concentrations of the monitored species. The coupling of the electronic tongue with the automation features of the flow‐injection system (ET‐FIP) allowed us to accurately characterize the biosorption process, through obtaining its breakthrough curves. In parallel, fractions of the extract solution were analyzed by atomic absorption spectroscopy in order to validate the results obtained with the reported methodology.