Residual Cr Concentration Research Articles

Eco-benign preparation of biosorbent using Momordica Charantia for the efficient removal of Cr(VI) ions from wastewater

Abstract Environmental pollution is the major issue of 21st century. The toxic industrial effluents are crucially damaging aquatic environment, in the form of heavy metals, dyes and acids. The heavy metals are toxic, carcinogenic, non-degradable and therefore must be removed to save natural environment and human health. Batch sorption efficiency of Momordica Charantia L. stem and root (MCS and MCR) was studied for Cr(VI) metal ions removal under controlled adsorption parameters. The adsorbed and residual concentration of Cr(VI) was determined by atomic absorption spectrophotometer (AAS). The adsorbent surface morphology was determined by FTIR, BET, SEM and elemental analysis by EDX. The Freundlich and Langmuir equilibrium isotherm and pseudo 1st and 2nd order kinetic models were studied to understand bio-sorption mechanism. The Freundlich isotherm and pseudo 2nd order kinetic was best fitted model for MCS and MCR bio-sorption process. The maximum Langmuir adsorption capacity (q max) was 312.50 and 400 (mg/g) for MCS and MCR respectively. The trend of removal efficiency (%) and metal uptake (q e) was in order as MCS > MCR. All data was statistically analyzed using mean values ± standard deviation (SD). In conclusion, MCS and MCR are suggested as excellent sorbents for the elimination of numerous contaminants from the wastewater.

Adsorptive Removal of Low-Concentration Cr(VI) in Aqueous Solution by Mg–Al Layered Double Oxides

To explore the adsorption removal mechanism of Mg-Al layered double oxides (LDOs) for low-concentration (≤ 5mg L-1) Cr(VI), the adsorption kinetics, adsorption isotherms and its influencing factors were studied by batch experiments. Cr(VI) adsorption reached equilibrium after 6, 11 and 15h for initial Cr(VI) concentrations of 1, 3 and 5mg L-1, respectively, and the final adsorption efficiency exceeded 99.0%. The residual concentration of Cr(VI) was within the allowable limit of Drinking Water Quality Standard of World Health Organization (0.05mg L-1). The experimental data fitted the pseudo-second-order and Freundlich models well. Mg-Al LDOs showed effective adsorption efficiency in the range of pH 3-9, and the adsorption efficiency was influenced by anions competition (HPO42- > SO42- > CO32- > NO3- > Cl-). The analyses of XRD, SEM and FT-IR spectra suggested adsorption Cr(VI) on Mg-Al LDOs was caused by capturing dichromate ions to reconstruct its structure. Therefore, Mg-Al LDOs is promising adsorbents for the low-concentration Cr(VI) treatment in polluted surface water and groundwater.

Combined effects of nano-TiO2 and hexavalent chromium towards marine crustacean Artemia salina

There has been a significant increased concern of the impact of the toxicity of multiple contaminants in the marine environment. Thus, this study was aimed at determining whether the interaction between nano-TiO2 and Cr(VI) would modulate their toxic effects with the marine crustacean, Artemia salina. Nano-TiO2 agglomerated in artificial sea water (ASW) and readily formed micron-sized particles that settled down in the medium. The addition of Cr(VI) to nano-TiO2 aggravated their agglomeration through sorption of Cr(VI) onto nano-TiO2. This was reflected by a decrease in the residual concentration of Cr in the suspension. Acute toxicity tests performed using pristine nano-TiO2 (0.25, 0.5, 1, 2, and 4 mg/L) and Cr(VI) (0.125, 0.25, 0.5, and 1 mg/L) displayed a concentration dependent rise in the mortality of Artemia salina. To examine the effects of mixtures of nano-TiO2 and Cr(VI) on Artemia salina, two groups of experiments were designed. The former group studied the toxic effect of nano-TiO2 (0.5, 1, 2, and 4 mg/L) with a fixed concentration (0.125 mg/L) of Cr(VI). While the latter group studied the toxicity of Cr(VI) (0.25, 0.5, and 1 mg/L) with a fixed concentration (0.25 mg/L) of nano-TiO2. The toxic effects of nano-TiO2 was not significantly reduced at a fixed concentration of Cr(VI) but in contrast, a significant reduction in the Cr(VI) toxicity by fixed concentration of nano-TiO2 was observed. Toxicity data was well supported by an independent action model that proved the mode of action between nano-TiO2 and Cr(VI) to be antagonistic. Furthermore, ROS generation and measurement of antioxidant enzyme activities were also in line with toxicity results. From this study, the modification of Cr(VI) toxicity at fixed concentration of nano-TiO2 could have a huge impact on the reduction in Cr(VI) toxicity across trophic levels.

Highly efficient removal of Cr(III)-poly(acrylic acid) complex by coprecipitation with polyvalent metal ions: Performance, mechanism, and validation

The Cr(III)-organic complexes formed between Cr(III) and multifunctional group ligands, such as polyacrylate, are highly water soluble and difficult to be removed from wastewater by common treatments. A novel strategy for efficiently removing Cr(III)-poly (acrylic acid) complex (Cr(III)-PAA) from wastewater without introducing secondary pollution is proposed using a coprecipitation method with polyvalent metal ions. Al(III), Fe(III), Zr(IV), and Ti(IV) were combined with the carboxyl of Cr(III)-PAA to decrease hydrophilia and achieve fast and efficient coprecipitation. Cr(III)-PAA was efficiently removed from wastewater by using these polyvalent metal ions, especially at low pH, where the ions exist as monomer. The residual concentration of Cr(III) in treated wastewater under the optimized experimental condition was less than 1.0 mg/L. No Cr(VI) and negligible amount of polyvalent metal ions were detected in the treated wastewater, indicating that almost all of the ions coprecipitated with Cr(III)-PAA. No secondary pollution also occurred. The high reactivity between the polyvalent metal ions and Cr(III)-PAA and the sharp decrease in the hydrophilia of the complex contributed to its highly efficient removal from wastewater. Actual tannery wastewater containing Cr(III)-organic complexes with high solubility and stability was treated through coprecipitation with Al(III). A high Cr(III) removal efficiency of 99.0% was obtained. This work provides new insights into the removal of soluble Cr(III)-organic complexes from wastewater by using an environment-friendly and cost-effective method.

The sequestration of Cr(VI) by zero valent iron under a non-uniform magnetic field: An interfacial dynamic reaction

A non-uniform magnetic field was applied to sequester Cr(VI) with microscale zero-valent iron (ZVI). When the non-uniform magnetic field was applied, the average removal rate of Cr(VI) was increased and the lag phase was shortened with the increasing of magnetic field intensity. The instantaneous rate was fast at the beginning and about 40% of the Cr(VI) was sequestered rapidly when ZVI was added into the magnetic field system. Later, the sequestration rate of Cr(VI) was reduced and remained stable with time until Cr(VI) was removed completely. The instantaneous removal rate was positively correlated with ZVI dosage and the rate per unit mass of ZVI was 0.455 mg/(L·min·gZVI). The constant rate stage was not affected by the initial and the residual concentration of Cr(VI). In the case where no magnetic field was applied, the removal of Cr(VI) is a process in which ZVI is depassivated and its reactivity is restored continuously. The promotion of a magnetic field on the removal of Cr(VI) is mainly due to increasing the role of adsorbed reducing species of Fe2+ or Fe0 on the ZVI surface. Aging of ZVI under a magnetic field could enhance the release rate of Fe2+ in the initial 5 min though the remanence of this kind of ZVI had little effect on the enhancement of the sequestration of Cr(VI).

A salt-free pickling chrome tanning technology: Pretreatment with the collective polyoxyethylene diepoxy ether and urotropine

Abstract Chromium and chloride are the staple pollutants in chrome tanning process due to the inclusion of common salt and chrome tanning agent. To reduce the environmental impacts of chrome tanning, a salt-free chromium tanning technology has been developed and optimized based on the collective treatment of polyoxyethylene diepoxy ether and urotropine on laboratory as well as on pilot scale. The results indicated that, without the application of sodium chloride, the pelts could be protected from acidic swelling in pickling and chrome tanning by the treatment of polyoxyethylene diepoxy ether, catalyzed by urotropine. Being superior to conventional processes, chrome tanning process could be conducted in the novel pickling conditions and during the course of experimentation the chromium uptake rate was increased to 96.0% from 74.3%, the Cr offering was decreased to 0.53% from 1.16% whereas, the residual Cr concentration in the spent chrome tanning liquors was cut down to 77.1 mg/L from 1083.3 mg/L around. The emissions of chemical oxygen demand and total dissolved solid were also lessened by 15% and 42%. In the course of pilot scale experiments, the organoleptic and mechanical properties were found to be similar with the ones from conventional ones. This investigation provides an improved assimilated method of leather making with the complete elimination of sodium chloride in pickling and proposes a green pollution free alleyway to the leather industry.

Passion-fruit shell biomass as adsorbent material to remove chromium III from contaminated aqueous mediums

The aim of the study was to evaluate an adsorbent material based on passion-fruit shell biomass (PFSB) for chromium III removal from contaminated aqueous mediums, composed of distilled water and different concentrations of Cr(III), with a dose of 5 g of PFSB per liter. The residual concentration of Cr(III) in the treated mediums was determined by Atomic Absorption Spectrophotometry. A good adsorption process was carried out, achieving removal levels up to 85, 80, and 53% for solutions of 20, 50 and 200 ppm of Cr(III), respectively. The results showed an adequate fit to Langmuir and Freundlich models (R2 of 0.8864 and 0.7596, respectively), obtaining the following parameters qmax: 27.933 mg g−1and b: 0.029 (for Langmuir model), and k: 1.400 and n: 1.650 (for Freundlich model), with a good adsorbent-adsorbate interaction for Cr(III) according to FT-IR spectra. Therefore, the obtained results suggest that Cr(III) can be removed by more than 50% by using passion-fruit shell, which with a minimum treatment could be used as an adsorbent in the treatment of chromium-contaminated aqueous mediums.

PEMBUATAN KARBON AKTIF DARI CANGKANG BUAH KARET (Hevea brasilliensis) DENGAN AKTIVATOR H3PO4 DAN APLIKASINYA SEBAGAI PENJERAP Cr(VI)


 Activated carbon from lignocellulosic materials are renewable, abundant, and inexpesive. Rubber shell activated carbon that activated chemicaly has abilty to adsorp heavy metal. The purpose of this research is to study the effect of phosphoric acid concentration toward characteristics of rubber shell activated carbon, and its ability to adsorp Cr(VI). The materials used in this research are rubber shell, aquadest, and Cr(VI) solution. This research was started by impregnating rubber shell with phosphoric acid at 20%, 40% and 60% for 1 hour and then sample was carbonizated in furnace at 500oC for 1 hour. After that, activated carbon was applied to adsorp Cr(VI). The characteristic of surface area of rubber shell activated carbon are measured by BET method. Furthermore, the residual concentration of Cr(VI) was measured with Atomic Adsortion Spectrophotometer. The result shows that characteristics of rubber shell activated carbon such as moisture content, ash content, volatile matter have fulfilled National Standard of Indonesia (SNI) except ash content of activated carbon that activated by 20% phosphoric acid. Surface area of activated carbon has fulfilled the standard of commercial adsorbent. The largest adsorption capasity is obtained using Rubber shell activated carbon that activated by 40% phosphoric acid with adsorption percentage 96,67%.

A salt-free and chromium discharge minimizing tanning technology: the novel cleaner integrated chrome tanning process

Chrome tanning is the most important and widely used tanning method in leather manufacture up to now. However, simultaneously control of the severe contamination of large amount of chromium and chloride discharge, both of which are serious environmental concerns, is highly challenging with the conventional chrome tanning process. Consequently, the development of leather manufacture is being unsustainable. In order to minimize the emissions of chromium and chloride integrately, a salt-free and high exhaustion chromium tanning method was designed and optimized in both laboratory and pilot scale. The results indicated that, being superior to the conventional process, the chrome tanning process was conducted in a salt-free condition smoothly and the chromium absorbility was increased to 98% from 73% in the novel process. Then the Cr dosage was minimized from 1.16% to 0.61% and the residual Cr concentration in the spent liquor dropped below to 50 mg/L from above 1100 mg/L. The pilot-scale experiments verified that the novel method was acceptable in the aspects of organoleptic and mechanical properties of resultant leather, product style and cost. It is anticipated that the spent liquor containing a very small amount of chrome and chloride can be more easily disposed and the generation of chromium-containing sludge will be stoichiometrical much less. The established novel chrome tanning process satisfactorily solves the longstanding problems commercially and matches the integral requirements of the modern sustainable leather industry.

Two-dimensional titanium carbide for efficiently reductive removal of highly toxic chromium(VI) from water.

Two dimensional (2-D) Ti3C2Tx nanosheets are obtained by etching bulk Ti3C2Tx powders in HF solution and delaminating ultrasonically, which exhibit excellent removal capacity for toxic Cr(VI) from water, due to their high surface area, well dispersibility, and reductivity. The Ti3C2Tx nanosheets delaminated by 10% HF solution present more efficient Cr(VI) removal performance with capacity of 250 mg g(-1), and the residual concentration of Cr(VI) in treated water is less than 5 ppb, far below the concentration (0.05 ppm) of Cr(VI) in the drinking water standard recommended by the World Health Organization. This kind of 2-D Ti3C2Tx nanosheet can not only remove Cr(VI) rapidly and effectively in one step from aqueous solution by reducing Cr(VI) to Cr(III) but also adsorb the reduced Cr(III) simultaneously. Furthermore, these reductive 2-D Ti3C2Tx nanosheets are generally explored to remove other oxidant agents, such as K3[Fe(CN)6], KMnO4, and NaAuCl4 solutions, by converting them to low oxidation states. These significantly expand the potential applications of 2-D Ti3C2Tx nanosheets in water treatment.

Carbothermal preparation of porous carbon-encapsulated iron composite for the removal of trace hexavalent chromium

Abstract Porous carbon-encapsulated iron (Fe@PC) composite was prepared through carbothermal reduction of Fe(NO3)3 and starch. The porous carbon could envelop iron and protect it from being oxidized, while iron endow the composite with ferromagnetism, so that Fe@PC can be easily recovered by an external magnetic field. The prepared material was used to remove trace Cr(VI) in polluted water. The Cr(VI) removal process of Fe@PC, which highly depended on both microporous structure and reducing groups, was significantly affected by the preparation conditions and solution pH. At 25 °C, Fe@PC-750 could remove 99.5% Cr(VI) from simulated wastewater containing 5.00 mg L−1 Cr(VI) with an initial pH of 7, and the residual concentration of Cr(VI) was as low as 0.02 mg L−1. The XPS analysis results confirmed that Cr(VI) could be reduced to Cr(III) after being adsorbed, and the elevation of pH would enhance the reduction ability of Fe@PC. The Fe@PC composite with high Cr(VI) removal efficiency, strong magnetic property and desirable regeneration ability can be practically applied in the removal of trace heavy metal pollutants from wastewater.

Development of a Wastewater Treatment System for Chromium Removal Using Chitosan

This study attempts to evaluate the removal of chromium from aqueous solution using chitosan as an adsorbent. The experiment was conducted by varying chitosan dosage (10-30 mg), pH (5-8), contact time (10-90 min) and agitation speed (50-250 rpm). The initial Cr concentration was fixed to 20 mg L-1. The results indicated that pH is the most significant factor that affects the removal of Cr. The R2 of 0.9963 showed that the overall model is good as the experimental values are close to predicted values. The optimized conditions obtained at 28.79 mg chitosan dosage, pH 6.40, 20.20 min contact time and agitation speed of 156.20 rpm. This optimum condition obtained to achieve 0.05 mg L-1 residual Cr concentration or 99.75% removal that meets Department of Environment Malaysia (DOE) effluent discharge requirement. The design of treatment system that consists of rapid mix, sedimentation and filtration unit is based on the optimum operating conditions. Rapid mix tank was designed with surface area of 9.18 m2 and volume of 27.8 m3. Sedimentation basin was designed with surface area of 100 m2 and volume of 83.33 m3. Filtration was designed with surface area of 16.67 m2.

Investigation of Dissolution and Precipitation Behaviours of Precipitates in Welded Joints of High Cr Ferritic Heat Resistant Steels

This paper is aimed at investigating dissolution and precipitation behaviour in fine grained heat-affected zones (FGHAZ), coarse grained heat-affected zones (CGHAZ), and base metals for the welded joints of high Cr ferrite heat resistant steels. The simulated HAZ (SHAZ) specimens were used, whose thermal cycles were controlled to be the same as those in the actual welded joint with peak temperatures of 1 173 and 1 523 K to represent FGHAZ and CGHAZ, respectively. The behaviours of dissolution and precipitation during welding, PWHT and ageing processes were observed. SEM observation showed that after long time ageing the precipitates in FGHAZ specimens (1 173 K) were fewer and larger than those in CGHAZ (1 523 K) specimens and base metal specimens. This phenomenon implied that growth and coarsening of precipitates in FGHAZ may play a role in the deterioration of creep property and Type IV cracking, which was observed in previous creep tests. X-ray diffraction analysis for the electrolytic extraction showed that the types of precipitates were M23C6, M7C3, MX, Laves phase, and μ phase. By using software of Thermo-Calc and Dictra, a 3-D model was performed to simulate the dissolution process of M23C6 during welding. It was found that the dissolution of M23C6 can lead to high Cr and high W concentration in a local region. On the other hand, the precipitation behaviour of M23C6 was simulated, and it was found that the growth of M23C6 was fast and in the period of PWHT and creep process it can reach to the equilibrium concentration in a short time of about 2 000 seconds. At last, the growth of Laves phase was simulated and it was found that it grew very slowly and it reached the equilibrium concentration in about 3 000 hours. As an important point, the simulation result showed that Laves phase was easy to grow in the region where M23C6 had dissolved due to the high residual concentration of Cr and W.