Removal of hexavalent chromium from wastewaters by bone charcoal

The adsorption of hexavalent chromium onto bone charcoal was studied as a function of time, amount of charcoal, pH, concentration of chromium and sample volume. The cross interference with other elements was also investigated. Tests were carried out with solutions of chromium(VI) at concentrations between 5 and 25 mg · L^–1. Chromium removal efficiencies higher than 90% were achieved at pH = 1 using 2 g of bone charcoal and a stirring time in the order of 30 min. Acid and alkaline pretreatments of bone charcoal did not improve the sorption capacity of bone charcoal against Cr(VI). The presence of other ions had practically no influence on the chromium removal. The presence of a matrix of tannery effluents did not reduce the removal capacity of bone charcoal for Cr(VI), but it was confirmed that only 47% of Cr(III) can be removed using these conditions. Received: 20 July 1998 / Revised: 4 October 1998 / Accepted: 10 October 1998     

Speciation of chromium in the waste water from a tannery

Due to the different toxicity of chromium (VI) and chromium (III) and the different toxicity of free hydrated metal ions versus stable complexes of the ions, the determination of the physicochemical form of the chromium is necessary in addition to the total metal content. In this investigation a strategy of analysis has been developed which provides information about the physicochemical form, toxicity and ecochemical behaviour of the chromium in the waste water. The strategy was used for the analysis of two waste water samples. The investigations were not able to give exact quantitative results for the different species initially present because each method shifted the equilibrium state. It was shown that the more toxic chromium (VI) species was unstable in both the waste water samples investigated. Although the two waste waters came from very different sources, most of the chromium (III) in both waste waters after centrifugation were not free ionic species but were associated with macromolecular particles (complexed or colloidal). 36% and 46% of the total chromium of the two samples was bound in a very stable complex; 25% and 15% was bound as colloids. Only a small part of the chromium was ionic (and hence particularly toxic). Despite the stable binding, most of the chromium could be coprecipitated with Fe(OH)₃ or Al(OH)₃ in laboratory experiments and would probably be mineralised in natural water.     

Thermodynamics of cleaning-up of waste waters polluted by chromium

The effect of Cr(VI) on Desulfovibrio vulgaris strain Hildenborough bioenergetic metabolism was monitored by microcalorimetry and the concomitant reduction of this metal was studied. Results showed that Cr(VI) is reduced by the bacterium and that the bacterial growth is altered, involving a strong modification of the metabolism of the bacteria. An absence of correlation between Cr(VI) reduction and cell growth is observed, suggesting that Cr(VI) does not yield energy to support anaerobic growth. The analysis of the enzymatic characteristics of Cr(VI) reduction are in progress. This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of charcoal from agriculture waste in the speciation of iodine from well and river waters

The concentrations of iodine in fresh waters are known to be within the range of 0.5 to 35 ng·ml⁻¹, much lower than in oceanic waters. The iodine concentrations, particularly that of¹²⁹I which is significant from the radiation safety aspect, in public drinking waters have to be specified in order to verify the required level before distribution for domestic use. A modified version of an established method was used in the adsorption of iodine, iodate, total inorganic iodine and charcoal-adsorbable iodine using activated carbon prepared from oil palm kernel wastes. A thorough investigation of the physical properties of the activated carbon was carried out to determine its viability as an adsorbent for volatile species such as iodine. The iodine species were preconcentrated from water samples collected from wells in villages and from water intake points along rivers. The quantitative analysis of the species adsorbed was done by irradiating the activated charcoal loaded with the respective species in a neutron flux of 5.1·10¹² n·cm⁻²·s⁻¹ from a TRIGA MkII, nuclear reactor. Recovery experiments using spiked samples was done to provide quality assurance controls.     

Removal of methylene blue by tea wastages from the synthesis waste waters

The tea wastages could remove methylene blue（MB） as a cationic dye from waste water corresponding to second-order kinetic model.Thermodynamic studies showed that adsorption equilibrium constant（K_L） and maximum adsorption capacities(Q_max) were increased with increasing temperature.The removal efficiency of MB for Co 0.01 mmol/L at optimum conditions was about 85%. The maximum uptake capacity(Q_max) of methylene blue in a batch reactor was 0.328,0.542 and 0.659 mmol/g at 15,25 and 40℃, respectively.The enthalpy change（ΔH） and entropy change（ΔS） were 11.356 kJ/mol and 20.563 J/（mol K）,respectively.     

Separation of sodium ions from trivalent chromium by electrodialysis using monovalent cation selective membranes

Trivalent chromium Cr(III) in wastewaters produced by leather tanning processes must be treated before discharge in the environment. Electrodialysis was studied for this application. Cr(III) ion is separated from sodium ion by using modified cation-exchange membranes. The membrane modification consists of a polyethylenimine layer electrodeposited on the membrane surface. This layer is positively charged in acidic media and repels multivalent ions while monovalent ions cross the membrane. The modified membrane in this study was a Nafion^® 324 membrane. The transfer of chromium, sodium, calcium, magnesium, chloride and sulphate ions from a mixture was investigated. The pH must be regulated in order to avoid chromium hydroxide precipitation in the dilute chamber. The behaviour of sulphate chloride system is unusual for the AMX membrane. Adsorption of PEI on the membrane surface is assumed to explain this behaviour. The overall current efficiency was close to 96–98% for cations and anions.     

Removal of chromium(VI) from wastewater using Sorel's cement

Summary Synthetic Sorel's cement [3Mg(OH)₂ ^. MgCl₂ ^. 8H₂O], is used as a new adsorbent material for removal of chromium(VI) ion from wastewater effluents. Parameters including contact time, adsorbent dosage and pH are examined and optimized. The equilibrium data are fitted very well to the Langmuir and Freundlich isotherms rather than linear. The adsorption isotherm indicates that the monolayer coverage is 21.4 mg Cr(VI) ion per g of Sorel's cement. The adsorbent is considered as a better replacement technology for removal of Cr(VI) ion from aqueous solutions due to its low cost, good efficiency, fast kinetics, and simple preparation. It offers remarkable efficiency for Cr(VI) removal from wastewater compared with many other natural and synthetic adsorbents.     

Application of Brazilian sawdust samples for chromium removal from tannery wastewater

Brazilian sawdust samples (Caryocar spp.; Manilkara spp.; and Tabebuia spp.) have been used for Cr(VI) adsorption from water. The series of adsorption isotherms were adjusted to modified Langmuir equation. Thermodynamic data of interactions were studied by the calorimetric titration of Cr(VI) in aqueous solution. All liquid/solid interface adsorptions were entalpically and entropically driven. These sawdust samples were also used to remove chromium from tannery wastewater. The application of Caryocar spp.; Manilkara spp.; and Tabebuia spp. reduced the amount of chromium from 2.11 ± 0.18 mg L⁻¹ to 1.15 ± 0.10; 0.29 ± 0.02 and 0.26 ± 0.02 mg L⁻¹, respectively.     

Investigation of tannery liming waste water using green synthesised iron oxide nano particles

ABSTRACT

The present study aimed that non-toxic, less expensive, easily available, safer to environment and previously unreported Eclipta prostrata leaf extract is used for the green synthesis of iron oxide nano particles. The iron oxide nanoparticles (NPs) were characterised by UV–visible, Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tannery effluents treated by photodegradation process and the removal efficiency of chemical oxygen demand (COD), biological oxygen demand (BOD) and sulphide were analysed. The maximum removal efficiency correlated with operating parameters was explained using response surface methodology with Boxmen Beckmen design.     

Instrumental evidence for biodegradation of tannery waste during vermicomposting process using Eudrilus eugeniae

Animal fleshing (ANFL) is the main solid waste generated during manufacturing leather, which should be disposed friendly to the environment. The effect of epigeic earthworm Eudrilus eugeniae (with and without addition) to transform fermented ANFL in solid state (SSF) and submerged state (SmF) mixed with cow dung and leaf litter into value added product was studied in a vermibioreactor at low residence period (25 days). The products were characterised for pH and C:N ratio and the results were declined at the end of the treatment process with significant reduction in earthworm processed product. The maturity and the chemical changes of the final products were determined using spectroscopic analysis as UV–Visible Spectroscopy in which worm products (vermicompost) reached >5; this indicated that they were well humified. The FT-IR analyses results confirmed the complete mineralisation of polypeptides, polysaccharides, aliphatic methyl groups and lignin, and formation of a deep nitrate band in worm product compared to without worm processed product. Thermogravimetry (TG) and differential scanning calorimetry analyses were carried out in the initial mixture and final products to identify the mass loss and quantitative and qualitative information regarding physical and chemical changes occurred during composting process. The overall results indicated that the maturity of vermicompost (with worms) was in the order SSF > SmF > control. The results indicate that the combination of both fermentation and bacterial/vermicomposting (without worms/with worms) reduced the overall time required for production of well humified organic manure especially with worms.     

Speciation of chromium in waste waters by coupled column ion chromatography-inductively coupled plasma mass spectrometry

An application of coupled column ion chromatography (IC)-inductively coupled plasma mass spectrometry (ICP-MS) is presented for speciation of chromium in waste waters. By coupling an anion column with a cation column, both the cationic Cr(III) and anionic Cr(VI) species can be analyzed with detection limits below 0.5 μg/1. The separation of the interfering ions (chloride, chlorate, perchlorate, sulphate, sulphite, sulphide, thiosulphate, carbonate, cyanide and some organic compounds) from the chromium peaks is discussed, and the use of different chromium isotopes for data acquisition is compared. Based on the results, m/z 52 was considered as an ideal isotope for speciation of chromium in waste waters by the coupled column IC-ICP-MS, because it did not suffer from polyatomic interferences and due to the high sensitivity for chromium. The analysis of the waste water samples should be performed as soon as possible after sampling according to the stability tests of the species.     

改性竹炭脱除贝类酶解液中的重金属镉

以蚶子贝肉酶解液为材料,利用聚天冬氨酸(PAsp)改性的竹炭吸附脱除酶解液中的重金属镉。考察了pH、脱除时间、竹炭投加量和温度对酶解液中镉脱除率的影响,并在单因素试验基础上通过响应面法确定了镉的最佳脱除条件。当pH为5.0、反应时间为25min、竹炭投加量(10m L酶解液)为0.26g,重金属镉的脱除率可达96.59%。研究表明,PAsp改性竹炭能显著提高吸附重金属的效率和能力,可用于脱除蚶子贝肉酶解液中的镉。     

Removal of actinides and fission products activity from intermediate alkaline waste using inorganic exchangers

Hydrated iron oxide or amorphous-Fe₂O₃·3.5 H₂O (HFeO), hydrated titanium oxide (HTiO) and hydrated thorium oxide (HThO) were synthesized and their applicability for the decontamination of intermediate level liquid wastes (ILLW) was tested. The sorption of a few actinides like plutonium and americium on HFeO, ¹³⁷Cs and ¹⁰⁶Ru on HTiO and ⁹⁰Sr on HThO was investigated as a function of pH, time and loading capacity of the hydrous oxide with metal ions. The influence of the total dissolved salt content was also monitored. Some of these parameters influenced the sorption behavior significantly. The radiation stability of these inorganic sorbents were studied by irradiating them up to 48 Mrad. Adsorbed actinides and fission products were successfully eluted from HFeO and from the mix-bed of HTiO and HThO by 0.5M nitric acid.The authors wish to thank Shri R. D. Changarani, Chief Superintendent NRG Facilities and Shri P. K. Dey, Head FRD for their valuable advice and constant support.     

Removal of actinides and fission products activity from intermediate alkaline waste using inorganic exchangers

Hydrated iron oxide or amorphous-Fe₂O₃·3.5 H₂O (HFeO), hydrated titanium oxide (HTiO) and hydrated thorium oxide (HThO) were synthesized and their applicability for the decontamination of intermediate level liquid wastes (ILLW) was tested. The sorption of a few actinides like plutonium and americium on HFeO, ¹³⁷Cs and ¹⁰⁶Ru on HTiO and ⁹⁰Sr on HThO was investigated as a function of pH, time and loading capacity of the hydrous oxide with metal ions. The influence of the total dissolved salt content was also monitored. Some of these parameters influenced the sorption behavior significantly. The radiation stability of these inorganic sorbents were studied by irradiating them up to 48 Mrad. Adsorbed actinides and fission products were successfully eluted from HFeO and from the mix-bed of HTiO and HThO by 0.5M nitric acid.The authors wish to thank Shri R. D. Changarani, Chief Superintendent NRG Facilities and Shri P. K. Dey, Head FRD for their valuable advice and constant support.     

Factors affecting the sorption of trivalent chromium by zeolite synthesized from coal fly ash

This research was initiated to determine the effects of different constituents and properties of zeolite synthesized from fly ash (ZFA) on Cr(III) sorption. The uptake of Cr(III) by ZFA was influenced greatly by pH, increasing with the increase in pH. The pH was controlled mainly by calcium-related components (especially CaCO3 and free CaO) and zeolite components in ZFAs. Sorption maximum of Cr(III) (Qm), determined by a repeated batch equilibration method, ranged from 22.29 to 99.91 mg/g for the 14 ZFAs. The Q(m) value correlated significantly with Ca-related components. The correlation coefficients were 0.9467, 0.5469, 0.7521, and 0.9195 for total Ca, CaCO3, CaSO4, and f.CaO, respectively. The Qm value was also closely related to cation-exchange capacity (r=0.6872) and specific surface area (r=0.7249). Correlation coefficients of Qm with dissociated Fe2O3 and Al2O3 were much higher than those of total Fe and total Al contents, respectively. It was suggested that, in ZFAs, zeolite and iron oxide acted as ion exchanger and adsorbent for Cr(III), respectively, while Ca components elevated the pH of the reaction system and consequently promoted ion exchange and adsorption and caused the surface precipitation of chromium hydroxide.     

Removal of137Cs from an intermediate level liquid waste by using various ion-exchange media

An intermediate level liquid waste (ILLW or Category III waste) stream was treated for the removal of radioactive Cs in pilot scale experiments, using three different ion exchange media. Results indicated that the polyacrylic fibre coated with cupric ferric hexacyanoferrate (CuFeHCF-fibre composite) was the most efficient, followed by cupric hexacyanoferrate loaded ion exchange resin (CuHCF-resin) and mixed zeolites (AR-1, 4A and 13X in the ratio 6:1:1). The mixed zeolites column and the CuFeHCF-fibre column were used in series in order to get a high total decontamination factor (DF). Leaching studies on the CuFeHCF-fibre composite loaded with¹³⁷Cs, in demineralised (DM) water, tap water and ground water media indicated a release of about 19.3%, 25.5% and 41.3% of¹³⁷Cs, respectively, in a period of about 8 months. XPS studies with CuFeHCF-fibre composite indicated some chemical interaction between the CuFeHCF precipitate and the polyacrylic fibre. Some of the possible disposal options for the CuFeHCF-fibre composite have also been discussed.