Total Cr Removal Research Articles

Optimum condition for the removal of Cr(VI) or total Cr using dried leaves of Pinus densiflora

A novel biomass, dried leaves of Pinus densiflora, showed very good performance in removing mutagenic Cr(VI) from aqueous solution in this study. Analytical results for different chromium species in aqueous and solid phases indicated that the mechanism of Cr(VI) removal by the biomass was ‘adsorption-coupled reduction’. Among various parameters of batch operation, pH, temperature and contact time significantly affected Cr(VI) removal and total Cr removal individually. As a result, optimal condition for the Cr(VI) removal was not equal to that for the total Cr removal. To examine the individual effects of these parameters on the Cr(VI) and total Cr removals statistically, therefore Box–Behnken model for experiment design and second-order polynomial model for fitting experimental data were used in this study. The removal efficiency of Cr(VI) increased with a decrease in pH or with increases of temperature and contact time until equilibrium had been attained. Meanwhile, an optimum pH existed for the total Cr removal efficiency, but increased with the increases of temperature and contact time. With 60h of contact time, 100% of Cr(VI) removal and >95% of total Cr removal could be obtained at pH 4 and 40°C.

Selecting an Effective Extractant for Removing Cr from Contaminated Soil

The effects of various extractants removing Cr from the soil of chromite ore processing residue (COPR) deposited sites were studied in order to select the optimal extractant agent. The effects of this agent on the removal of Cr(VI) and Cr(III) in the contaminated soil were also investigated. The results showed that organic complexing agents had higher removal efficiency than that of inorganic complexing agents due to the high content of Cr(III) in the soil(90.3%). The Cr removal of citric/sodium citrate (mole ratio: 1:1) was 35.95% in 24h. The reason why citric/sodium citrate removed more Cr than other agents is that citric can solubilize the mineral matrix, compete for the surfaces sites to desorb Cr(VI) and remove Cr(III) by its complexation. The concentration radio of Cr(VI) and Cr(III) in the initial soil was 0.11. Thus improving the removal of Cr(III)is the key point of improving the total Cr removal.

STUDIES ON ADSORPTION AND BIODEGRADATION OF CHROMIUMCONTAINING WASTEWATER BY LABORATORY-SCALE SEQUENCING BATCH REACTOR-POWDERED ACTIVATED CARBON SYSTEM

The study involved investigating the effects of Cr(III) and the efficacy of powdered activated carbon (PAC) in reducing the inhibitory effects of Cr(III) on activated sludge under sequencing batch reactor (SBR) operation. The addition of Cr(III) into SBR system caused significant inhibitory effects on the activity of activated sludge as indicated by drastic drop in specific oxygen uptake rate (SOUR). The increase of Cr(III) concentration from 5 to 10 mg/L further deteriorated the treatment performance of SBR system in terms of the total organic carbon (TOC), suspended solids (SS) and Cr(III) removal efficiencies. With 0.167 g/L PAC (0.5 g PAC/cycle) addition into the SBR reactor influent wastewater, the TOC and Cr(III) removal efficiencies were improved from 88 to 94 % and 82 to 90 %, respectively. Coupled with the increasing mixed liquor biomass suspended solids concentration after PAC addition, the biomass apparently played the key role in the uptake of Cr(III) and kept the effluent Cr(III) concentration low. The addition of PAC was an effective way to allow continuous operation of the biological process in the presence of Cr(III) as indicated by increased SOUR as well as Cr(III) and TOC removal efficiencies.

Reduction and removal of Cr(VI) from aqueous solutions using modified byproducts of beer production

Biosorption, as an effective and low-cost technology treating industrial wastewaters containing Cr(VI), has become a significant concern worldwide. In this work, acid-modified byproducts of beer production (BBP) were used to remove Cr(VI) from aqueous solutions. Removal of Cr(VI) increases as the pH is decreased from 4.0 to 1.5, but the maximum of total Cr removal is obtained in a pH range from 2.0 to 2.5. Nearly 60% of the initial Cr(VI) (100mgL−1) was adsorbed or reduced to Cr(III) within the first 10min at pH 2.0. The Cr(VI) removal capability of acid-modified BBP materials was almost completely retained after regenerating with acid. FT-IR and XPS spectra revealed that carboxylate and carboxyl groups on the surface of modified BBP materials play a major role in Cr(VI) binding and reduction, whereas amide and other groups play a minor role in the Cr(VI) removal process.

Pretreatment of actual high-strength phenolic wastewater by manganese oxide method

This paper deals with treating high phenol-concentrated wastewater from coal gasification by manganese oxide method. Mixed-phase manganese oxides of manganite and hausmannite were synthesized with industrial MnSO 4 and NaOH by air oxidation. The effects of sulfuric acid dosage, reaction time, temperature, manganese oxide grain size and concentration on removal efficiency of total phenols were studied with laboratory bench-scale experiments. The results indicated that the removal process was more effective under the experimental conditions, i.e. acidified media at pH < 4 and an excessive amount of fine particles with a long reaction time. Solution pH and manganese oxide concentration were two of the most important factors which should be well regulated to guarantee higher removal rate. The mixture of manganite and hausmannite showed improved activity for removal of total phenols, TOC and COD Cr as compared with MnO 2 (AR) but similar to cryptomelane and K-birnessite. Most of organic contaminants especially phenol which occupied absolute predominance in initial wastewater were removed to enhance the biodegradability for further biological treatment. This investigation will provide fundamental method for developing a pretreatment method of industrial phenolic wastewater with flexibility, simplicity and high activity.

Biosorption of chromium from aqueous solution and electroplating wastewater using mixture of Candida lipolytica and dewatered sewage sludge

In this study, the objective was to investigate Cr removal from aqueous solutions, as well as Cr, Cu, Ni and Zn from electroplating wastewaters by the mixture of Candida lipolytica and sewage sludge. The bioreduction ratios of Cr(VI) and the removal ratios of total Cr showed that initial pH, biosorbent dosage and contact time were the important parameters for Cr biosorption. The range of optimal pH for the mixture (1–5) was wider than C. lipolytica (1–4) and sewage sludge (2–4), respectively. Biosorption and bioreduction potentials of living C. lipolytica were better than those of cell wall and cytoplasm. Bonded hydroxyl group, CH 2 asymmetric stretch, amide I, amide II, amide III, secondary amide, pyridine(I)β(C–H) and pyridine(II)β(C–H) were detected in the biosorbent and they were the functional groups for binding Cr. The effect of Cu and Zn in combination was significant on the removal of total Cr and the bioreduction of Cr(VI).

Optimum pHs for Cr(VI) co-removal with nucleated Cu(II) precipitation in continuous-flow fluidised metal strippers

A compact nucleated precipitation technology using two fluidised sand columns in series was developed to pretreat model metal-plating wastewater containing high concentrations of Cu(II) and Cr(VI). Since either Cu(II) precipitation or Cr(VI) co-removal with Cu(II) precipitation was found to be highly pH dependent in batch tests, the continuous-flow studies were conducted under different pHs. Experimental results show that high pH has no positive influence on either Cr(VI) or Cu(II) removal in the continuous-flow fluidised metal stripper technology. Operation at pH 6.5 in both columns can obtain significantly higher levels of both total Cr(VI) and total Cu(II) removal compared with work at pH 9.5 in both columns and work at pH 6.5 and 9.5 in the 1st and 2nd columns, respectively

Enhancement strategies for Cu(II), Cr(III) and Cr(VI) remediation by a variety of seaweed species

Various chemical treatments have been applied to six brown, red and green seaweed species with a view to enhancing their metal removal for Cu(II), Cr(III) and Cr(VI). Treatment with acetone resulted in the greatest enhancement for both cationic and anionic species with relatively low mass losses (15–35%), indicating its low risk to biomass operational stability. Cation binding was increased by 69%, while the total Cr removal was augmented by 15%. Cr(VI) binding was shown to be an adsorption-coupled reduction, whereby Cr(VI) was bound to the biomass surface at pH 2 and subsequently reduced to Cr(III). Acetone treatment also resulted in biomasses that were capable of converting up to 83% of Cr(VI) in solution to Cr(III). Blocking of carboxyl and amino functionalities had significant negative effects both on total Cr removal as well as percentage conversion of Cr(VI) to Cr(III). Results therefore indicated the significant role played by these moieties in metal binding to these seaweeds. Potentiometric titrations displayed agreement between the degree of esterification and the decrease in Cu(II) removal for Ulva spp. and Polysiphonia lanosa. FTIR analysis identified changes in biomass functionality and availability after chemical modification, the results of which were in agreement with metal removal studies. In conclusion, these biosorbents represent suitable candidates to replace conventional removal technologies for metal bearing wastewaters, in particular for the detoxification of hazardous Cr(VI) waste streams.

A novel study of hexavalent chromium detoxification by selected seaweed species using SEM-EDX and XPS analysis

Abstract The toxicity and mobility of Cr(VI) means that it is crucial that the amount of the heavy metal discharged in industrial waste streams is significantly decreased. Seaweed biomass represents a benign, cost-effective, sustainable and efficient solution for the detoxification of anionic Cr(VI) to the less hazardous cationic Cr(III). Chromium binding and reduction behaviour of three seaweeds, Fucus vesiculosus (brown), Ulva spp. (green) and Palmaria palmata (red), was investigated using a colorimetric method while the surface characteristics of the biomasses were examined using SEM/EDX and XPS techniques. This is the first study of red seaweeds for the detoxification of Cr(VI). Results indicated that F. vesiculosus and P. palmata had comparable total Cr removal efficiencies of approximately 18%, while Ulva spp. removed 14% Cr from a 2000 mg L −1 metal solution. Conversion of Cr(VI) to Cr(III) in solution ranged from 51% for F. vesiculosus to 34% for Ulva spp. over a 6-h period. SEM revealed considerable morphological differences between Cr(III) and Cr(VI)-loaded seaweeds while EDX results confirmed an ion-exchange mechanism for Cr(III) binding. XPS results indicated that significant quantities of Cr(VI) solution were reduced when placed in contact with the seaweed surface over a 6-h period, resulting in a 64–75% conversion to Cr(III) bound to the seaweed. Thus, the potential of these seaweeds to bio-reduce and detoxify elevated Cr(VI) concentrations over relatively short time periods has been demonstrated. Cr(VI) binding also altered the relative quantities of carboxyl and alcohol groups in biomass polysaccharides, thus indicating the importance of these functionalities in binding and reduction of Cr(VI) to Cr(III). This work, coupled with existing capacity data points towards the viability of these environmentally friendly biosorbents for use in packed columns in a number of industries including electroplating and tanning.

Effects of sodium hypochlorite and high pH buffer solution in electrokinetic soil treatment on soil chromium removal and the functional diversity of soil microbial community

Effects of sodium hypochlorite (NaClO), applied as an oxidant in catholyte, and high pH buffer solution on soil Cr removal and the functional diversity of soil microbial community during enhanced electrokinetic treatments of a chromium (Cr) contaminated red soil are evaluated. Using pH control system to maintain high alkalinity of soil together with the use of NaClO increased the electrical conductivities of soil pore liquid and electroosmotic flux compared with the control (Exp-01). The pH control and NaClO improved the removal of Cr(VI) and total Cr from the soil. The highest removal percentages of soil Cr(VI) and total Cr were 96 and 72%, respectively, in Exp-04 when the pH value of the anolyte was controlled at 10 and NaClO was added in the catholyte. The alkaline soil environment and introduction of NaClO in the soil enhanced the desorption of Cr(VI) from the soil and promoted Cr(III) oxidation to mobile Cr(VI), respectively. However, the elevated pH and introduction of NaClO in the soil, which are necessary for improving the removal efficiency of soil Cr, resulted in a significantly adverse impact on the functional diversity of soil microbial community. It suggests that to assess the negative impact of extreme conditions for enhancing the extraction efficiencies of Cr on the soil properties and function is necessary.

Laboratory-Scale Evaluation of Cr(VI) Removal from Clay by Electrokinetics Incorporated with Fe(O) Barrier

The effectiveness of incorporating Fe(O) barrier into electrokinetic (EK) process to remediate Cr(VI) contaminated clay (1,150mg∕kg) was investigated. The EK experiments were conducted using a 12cm long sample under a constant electric gradient of 2V∕cm for 144h. The barrier was installed in the cell and was filled with Fe(O) and silica sand (1:1w∕w). Experimental results showed the removal of Cr from clay was characterized by the high Cr(VI) concentration that occurred in the anode reservoir and the presence of Cr(III) precipitates in the cathode reservoir. The efficiencies of Cr(VI) reduction and total Cr removal for the EK process are 78 and 28%, respectively. As the barrier was installed in the process, a nearly 100% Cr(VI) reduction and 60–70% total Cr removal were achieved. The Cr removal mechanisms were mainly attributed to ion migration and electro-osmotic advection caused by electric gradient. Results indicated that the EK process was enhanced by the reduction of Cr(VI) to Cr(III) by Fe(O) in the barrier. The use of the Fe(O) barrier in EK technology is an effective process for the reduction of Cr(VI) from contaminated clay.

Modeling Chromium Dissolution and Leaching from Chromite Ore-Processing Residue

Chromium has been widely used in many industrial applications. As a result of chromite ore processing, large amounts of chromite ore processing residue (COPR) material that can be classified as hazardous have been produced and released into the environment. Therefore, knowledge of migration behavior and leaching rates of chromium through waste materials are of primary concern for environmentally sound management of hazardous wastes. Leaching rates of total Cr and Cr(VI) were studied experimentally using laboratory columns packed with COPR material produced by a sodium chromite plant. Based on the experimental results, the present study aims, through mathematical modeling, to understand the dissolution kinetics of chromium during leaching of COPR material and to investigate the effectiveness of intermittent leaching, which involves a sequence of batch (dissolution) and mass flushing (leaching) operational modes. Modeling results show that a coupled system of two first-order differential equations was able to capture the essential characteristics of leaching behavior of COPR material. In addition, the kinetics of chromium dissolution from COPR appeared to be controlled by the difference between aqueous phase concentration and saturation concentration (effective solubility), by the mass fraction of dissolvable chromium remaining in the solid phase, and finally, by the contribution of a constant dissolution rate manifested as a steady-state tailing behavior. As a result of performed simulations it was seen that intermittent leaching could be 65 and 35% more effective than continuous leaching for total Cr and Cr(VI) removal, respectively.

Treatability of chromite ore processing waste by leaching.

Developing treatment and disposal strategies and health-based clean-up standards for chromium containing wastes continues to be an important environmental regulatory issue because of the opposing solubility and toxicity characteristics of chromium species under diverse environmental conditions. In this study, leaching characteristics of total Cr and Cr(VI) were investigated using laboratory column studies. The data obtained from the experimental studies were analysed to assess the treatability of chromite ore processing waste (COPW) by leaching and to identify the leaching strategies that enhance mass removal rates of chromium species. COPW used for laboratory soil column studies was obtained from an industrial plant producing sodium chromate in Mersin, Turkey. Laboratory investigations involved chemical characterisation of waste material and column studies. For waste characterisation, U.S. EPA toxicity characterisation leaching procedure (TCLP) was performed on COPW to determine the concentrations of metal species in the TCLP extract. For column studies, various laboratory columns containing plain COPW material, 1:1 COPW/reducing agent (elemental iron or manure) mixture and different type soils (sand, loam and clay) overlain by COPW were subjected to leaching tests using acidic, neutral and alkaline influent water to determine Cr mass leaching efficiencies. Based on the TCLP analyses, COPW is classified as hazardous waste. As a result of comparing the leaching efficiency data from twelve leaching columns, the maximum removal of total Cr was achieved by leaching COPW/manure mixture using acidic (pH 4.78) influent water. The highest Cr(VI) leaching efficiency was achieved in the columns of plain COPW and COPW/manure mixture using highly alkaline (pH 12.0) influent water. The least effective leaching efficiency for both total Cr and Cr (VI) was obtained by leaching plain COPW with neutral (pH 7.0) influent water. Land-disposal of the treated COPW material by mixing with clayey soils seems to be a viable alternative.

Chromic acid removal by anion exchange

AbstractThe kinetics of dilute chromic acid removal by anion exchange was studied using a batch system. Rate model formulated for total Cr(VI) removal based on film diffusion control was applied. This rate model was shown to adequately fit the experimental rate data. In addition, column experimental runs were performed by using 20‐50 mesh anion resin with feed solution containing 0.2 g/L CrO3. The bed heights of 15, 25 and 35 cm and flow rates ranging from 1.02 cm/s to 2.38 cm/s were employed in the experiments. Linear driving force rate expression based on film diffusion rate control was incorporated in the model equations for simulation of column performance. The kinetic parameter and equilibrium relation in the rate equation were obtained independently either by separate experiments or from data available in the literature. Satisfactory agreements between experimental and calculated breakthrough curves were obtained.

Color variability in normal and gynogenetic progenies of ornamental (Koi) common carp ( Cyprinus carpio L.)

Photosynthetic bacteria have flexible metabolisms and strong environmental adaptability, and require cheap, but plentiful, energy supplements, which all enable their use in Cr(VI)-remediation. In this study, the effects of culture conditions on the total Cr removal rate were investigated for a newly identified strain of Rhodobacter sphaeroides SC01. The subcellular distribution and Cr(VI) reduction ability of four different cellular fractions were evaluated by scanning electron microscopy and transmission electron microscopy. Experiments indicated that the optimal culture conditions for total Cr removal included a culture temperature of 35 °C, pH of 7.20, an NaCl concentration of 5 g L−1, a light intensity of 4000 lx, and an initial cell concentration (OD680) of 0.15. In addition, most Cr was found in the cell membrane in the form of Cr (III) after reduction, while cell membranes had the highest Cr(VI) reduction rate (99%) compared to other cellular components. In addition, the physical and chemical properties of SC01 cells were characterized by FTIR, XPS, and XRD analyses, confirming that Cr was successfully absorbed on bacterial cell surfaces. CrPO4‧6H2O and Cr5(P3O10)3 precipitates were particularly identified by XRD analysis. After screening supplementation with five phosphor salts, Cr(VI) reduction due to bioprecipitation was improved by the addition of Na4P2O7 and (NaPO3)6 salts, with the Cr(VI)-reduction rate combined with Na4P2O7 addition being 15% higher than that of the control. Thus, this study proposes a new Cr(VI)-removal strategy based on the combined use of photosynthetic bacteria and phosphor salts, which importantly increases its potential application in treating wastewater.