María P. Elizalde-González

Sorption on natural solids for arsenic removal

Steady state experiments were conducted on arsenic sorption from aqueous solutions by natural solids to test the feasibility of these materials to act as concentrator for arsenic removal from groundwater and drinking water. The solids considered were natural zeolites, volcanic stone, and the cactaceous powder CACMM. The arsenic species studied were As(III), As(V), dimethylarsinic acid (DMA) and phenylarsonic acid (PHA). The arsenic removed was determined from the data obtained by measuring the concentration diminution of the arsenic species in the liquid phase at equilibrium before and after the adsorption experiment by means of ICP-AES for the total concentration of arsenic and IC-ICP-MS to determine the arsenic species. The latter method allowed the detection of As(V) additionally formed as a result of the oxidation of As(III) on some of the zeolites. The sorption of the arsenic species onto zeolites was studied on both non-activated and activated zeolites, as well as on zeolites hydrogenated or modified with iron, and with respect to varying pH. The kinetics and the ability to desorb and readsorb the arsenic species were investigated for selected zeolites.

Uptake of arsenite and arsenate by clinoptilolite-rich tuffs

Abstract Clinoptilolite-containing rocks were used to study the possible uptake of arsenite (H 3 AsO 3 ) and arsenate (H 2 AsO 4 − ) species from aqueous solution. Two samples also exhibited mordenite and erionite zeolitic phases. Batch and isotherm studies at pH 4 in the concentration range 0.1 −1 were performed. The experimental data were used to model Freundlich, Langmuir and Langmuir–Freundlich adsorption isotherms. Solutions were analyzed by means of ion chromatography coupled with inductively coupled plasma mass spectrometric detection (IC-ICP-MS). All zeolitic samples investigated removed more H 2 AsO 4 − than H 3 AsO 3 at equivalent arsenic concentrations. Although the saturation capacity of the tuffs studied was inversely related to the silicium dioxide content and directly to the iron content in the acid-washed zeolite, the addition of iron did not significantly improve the removal efficiency. Up to 98% of H 3 AsO 3 were removed from a 500 μg As l −1 solution by three of the samples studied after a contact time of 70 days.

Performance of mango seed adsorbents in the adsorption of anthraquinone and azo acid dyes in single and binary aqueous solutions.

In this study the husk of mango seed and two carbonaceous adsorbents prepared from it were used to study the adsorption behavior of eight acid dyes. The adsorbed amount in mmol m(-2) decayed asymptotically as the molecular volume and area increased. The interaction between the studied dyes and the mesoporous carbon was governed by the ionic species in solution and the acidic/basic groups on the surface. Less than 50% of the external surface of the microporous carbon became covered with the dyes molecules, though monolayer formation demonstrating specific interactions only with active sites on the surface and the adsorption magnitudes correlated with the shape parameter of the molecule within a particular dye group. The adsorption behavior in mixtures was determined by the molecular volume of the constituents; the greater the molecular volume difference, the greater the effect on the adsorbed amount. We also demonstrated that the raw husk of the mango seed can be used to remove up to 50% from model 50 mg l(-1) solutions of the studied acid dyes.

Detection of arsenic-containing hydrocarbons in canned cod liver tissue

Arsenic is a metalloid well known to be potentially toxic depending of its species. Lipid-soluble arsenicals (arsenolipids) are present in a wide range of biological samples in which they could play a role in the biosynthesis of organoarsenic compounds from inorganic arsenic compounds. Arsenolipids have recently attracted considerable interest. In order to gain deeper insights into the impact of arsenolipids new analytical approaches for reliable determination of this class of arsenic-containing hydrocarbons in various matrices are needed. High concentrations of arsenolipids were found in seafood which served as sample material in this study. We report the investigation of three arsenolipids found in canned cod liver from which they were extracted and purified by solid phase extraction (SPE) using a silica gel column and ethyl acetate/methanol as eluent. Analytical studies were conducted by means of gas chromatography coupled with ICP-MS, MIP-AES and EI-qMS and by TOF-MS. The results obtained by GC-ICP-MS and GC-MIP-AES showed the existence of numerous arsenic compounds in the SPE fractions collected. Three major peaks were found within a retention time window between 10 and 25 min. The presence of arsenic compounds in the fish tissue could be confirmed using GC-EI-qMS analysis. Corresponding information of the molecular weights of the major arsenic species were provided by TOF-MS which allows highly accurate mass determinations. The results showed the presence of the arsenic-containing hydrocarbons with the following molecular formulas: C(17)H(37)AsO (calculated for [M+H](+) 333.2133; found 333.2136; Deltam=0.90 ppm); C(19)H(41)AsO (calculated for [M+H](+) 361.2446; found 361.2446; Deltam=0.00 ppm); C(23)H(37)AsO (calculated for [M+H](+) 405.2133; found 405.2145; Deltam=2.96 ppm). Suggestions for the corresponding structures are discussed.

Application of natural zeolites for preconcentration of arsenic species in water samples.

Zeolites of the clinoptilolite type produced in Mexico and Hungary were investigated with respect to their sorption efficiency for various redox species of arsenic. Long-term experiments showed that arsenate remains stable for a long period in spiked deionised water and drinking water, as well as in the surface water of the Biela valley in Saxony, Germany. Both clinoptilolites are able to decrease the initial arsenic concentration of 200 microg l(-1) by more than 75% in deionised, drinking, ground and surface waters. In the case of the Mexican zeolite, both the arsenite and the arsenate concentrations (200 microg l(-1)) can be lowered from 200 microg l(-1) to 10 microg l(-1), which is the World Health Organisations (WHOs) recommended maximum level. It was found that the presence of cations and anions in the natural waters of Biela, Germany, and Zimapán, Mexico, did not reduce the efficiency of the selected zeolites. The Hungarian zeolite removed 75% of the arsenate in the Zimapán water and only 50% when the sample was first acidified. This zeolite totally desorbed the fixed arsenic into a water volume that was half the volume in the adsorption experiment.

Removal of acid orange 7 by guava seed carbon: a four parameter optimization study.

The preparation of carbon from waste materials is a recent and economic alternative for the removal of dyes. In this study four samples of carbon were obtained by thermal treatment at 1000 degrees C using as precursor the guava seed with different particle sizes. The Taguchi method was applied as an experimental design to establish the optimum conditions for the removal of acid orange 7 in batch experiments. The chosen experimental factors and their ranges were: pH (2-12), temperature (15-35 degrees C), specific surface area (50-600 m(2)g(-1)) and adsorbent dosage (16-50 mg ml(-1)). The orthogonal array L(9) and the larger the better response category were selected to determine the optimum removal conditions: pH 2, temperature 15 degrees C, S(esp) 600 m(2)g(-1) and dosage 30 mg ml(-1). Under these conditions a total removal of acid orange 7 was achieved. Moreover, the most significant factors were the carbon specific surface area and the pH. The influence of the different factors on the adsorption of acid orange 7 from solution is explained in terms of electrostatic interactions by considering the dye species and the character of the surface.

Guava seed as an adsorbent and as a precursor of carbon for the adsorption of acid dyes

The guava seed (SEGUVE) was characterized by ultimate and proximate analysis. In SEGUVE the principal thermal effect occurred at 363 degrees C and this can be attributed to the cellulose degradation, which was the main component ( approximately 61%). The guava seed has an acidic character with a high content of bulk functional groups (CO) and these characteristics were affected by carbonization. Two samples of carbon were prepared from the seeds at 600 and 1000 degrees C without chemical activation. Adsorption of eight acid dyes belonging to the monoazo and anthraquinone class was studied at 25 degrees C. The non-carbonized SEGUVE adsorbed the acid dyes more efficiently than SEGUVE-C600 and SEGUVE-C1000 although the specific surface of the raw material SEGUVE was low.

In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions

Adsorption methods have been developed for the removal of arsenic from solution motivated by the adverse health effects of this naturally occurring element. Iron exchanged natural zeolites are promising materials for this application. In this study we introduced iron species into a clinoptilolite-rich zeolitic tuff by the liquid exchange method using different organic and inorganic iron salts after pretreatment with NaCl and quantified the iron content in all trials by XRF spectroscopy. The materials were characterized by XRD, FTIR, FTIR-DR, UV-vis, cyclic voltammetry, ESR and Mössbauer spectroscopies before and after adsorption of arsenite and arsenate. The reached iron load in the sample T+Fe was %Fe(2)O(3)-2.462, n(Fe)/n(Al)=0.19, n(Si)/n(Fe)=30.9 using FeCl(3), whereby the iron leachability was 0.1-0.2%. The introduced iron corresponded to four coordinated species with tetrahedral geometry, primarily low spin ferric iron adsorbing almost 12 mug g(-1) arsenite (99% removal) from a 360 mug(As(III)) L(-1) and 6 mug g(-1) arsenate from a 230 mug(As(V)) L(-1). Adsorption of arsenite and arsenate reached practically a plateau at n(Fe)/n(Si)=0.1 in the series of exchanged tuffs. The oxidation of arsenite to arsenate in the solution in contact with iron modified tuff during adsorption was observed by speciation. The reduction of ferric iron to ferrous iron could be detected in the electrochemical system comprising an iron-clinoptilolite impregnated electrode and was not observed in the dried tuff after adsorption.

Removal of textile dyes from aqueous solutions by adsorption on biodegradable wastes

Abstract The adsorption of the textile dyes Basic Blue 41, Aniline Blue, Reactive Black 5 and Mariposa Blue was studied from model solutions prepared in distilled water in the concentration range up to 2000 mg 1–1. Biodegradable wastes were used and are proposed here as adsorbents due to their abundance and inexpensiveness in the authors’ country. The influence of the particle size, pH, presence of an electrolyte in the dye solution, adsorbent activation and competition in ternary dyes mixtures was determined in this study. Adsorption capacity of the adsorbents designated as HOMAP and POMAP with particle diameter less than 3 mm for the Basic Blue 41 dye was found to be 154 and 77 mg g‐1, respectively. The efficiency of the prepared adsorbents for removing basic, acid and reactive dyes with a concentration of 400 mg 1–1 was examined. A comparison of the adsorption capacity and desorption feasibility of the adsorbents was made. The basic dye was adsorbed with efficiencies varying from 87–98%, the reactive dye was removed in the range 60–98% and the add dye, 60–70% by three of the four adsorbents tested in this study. The determination of adsorption equilibrium concentrations was followed by HPLC with diode array detection.

Electrochemical treatment of textile dyes and their analysis by high-performance liquid chromatography with diode array detection

Several textile dyes were individually exposed to electrochemical treatment. Chromaticity variation and the formation of degradation products were followed using a UV spectrophotometer and HPLC with diode array detection. Dyes studied belong to the azo (color index, C.I. 15,510), methine (C.I. 48,013), indigo (C.I. 73,040), natural (C.I. 75,760) and arylmethane (C.I. 42,000) classes. Aliquots of the solutions treated at constant potential were analyzed and compared with control dye solutions. The final electrolysis solutions obtained by using different electrode materials: Pt, Ti and diamond presented different chromatograms. It was found that the novel (in this application) diamond electrode is efficient in studying the degradation of various dyes. Possible fragmentation and molecule moiety rearrangement are proposed as a result of the electrochemical treatment.