Electrochemical Cr(VI) reduction using a sacrificial Fe anode: Impacts of solution chemistry and stoichiometry

Chuang, Sheng-Ming,Ya, Vinh,Feng, Chiao-Lin,Lee, Shou-Jen,Choo, Kwang-Ho,Li, Chi-Wang Elsevier 2018 Separation and purification technology Vol.191 No.-

<P><B>Abstract</B></P> <P>A systematic investigation of Cr(VI) reduction using electrochemical reduction revealed that the Cr(VI) reduction was extremely fast with reaction kinetics limited by the anodic generation of Fe(II). The Cr(VI) reduction rate increased with decreasing pH at the initial stage of reaction but the time to reach complete Cr(VI) reduction is pH independent. The amount of Fe(II) generated per mole of Cr(VI) reduced was calculated and compared with the stoichiometric value, i.e., 3mole of Fe(II) needed per mole of Cr(VI) reduced. The values are 11.1% higher than the stoichiometric value for pH 7 and 9, but are 32.0% less for pH 3 and 5. The spontaneous reduction of Cr(VI) by Fe<SUP>0</SUP> and adsorption of Cr(VI) to Fe(OH)<SUB>3</SUB> precipitates might contribute the additional Cr(VI) removal. Effect of DO was investigated under various mixing schemes. Under N<SUB>2</SUB> purging, Fe(II) generated for one mole of Cr(VI) reduced is 3.67% higher than the stoichiometric value, while mechanic mixing and aeration mixing show 15% and 19%, respectively, higher than stoichiometric value, indicating that DO does impact Cr(VI) reduction. The electrochemical Cr(VI) reduction process was also employed to treat electroplating wastewater with and without pH pre-adjustment, achieving 100% total Cr and Ni removal for both cases. ORP can be used as a controlling parameter when electrochemical reduction is implemented for Cr(VI) reduction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of current on Cr(VI) reduction under same current density was studied. </LI> <LI> Effects of initial and fixed pH on Cr(VI) reduction were investigated. </LI> <LI> Effect of DO on Cr(VI) reduction was explored. </LI> <LI> Electrochemical reduction was applied for treating electroplating wastewater. </LI> <LI> ORP is an ideal parameter for controlling electrochemical Cr(VI) reduction. </LI> </UL> </P>

The removal of Cr(VI) from aqueous and saturated porous media by nanoscale zero-valent iron stabilized with flaxseed gum extract: Synthesis by continuous flow injection method

Neman Izadi,Banafsheh Haji Ali,Mohammad Sajjad Shahin,Majid Baghdadi 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.8

Recently, the in-situ removal of contaminants by iron nanoparticles has been considered due to their nontoxicity,abundance, ease of production, and cost-effectiveness, which can be accomplished by injecting them underground. In this study, nZVI was synthesized using a novel continuous synthesis method using flaxseed glaze as a green,non-toxic, and low-priced coating. The produced nanoparticles were characterized by dynamic diffraction analysis(DLS), field electron microscopy (FE-SEM), X-ray spectroscopy (EDX), and infrared spectroscopy (FTIR) spectroscopy. Batch experiments were conducted to evaluate the effect of Cr(VI) concentration, FG-nZVI dosage, pH, and coexistingcomponents (Total dissolved solids, Humic acid, and NO3) on Cr(VI) removal. Results of the characterization andidentification, and stability tests indicated that nanoparticles synthesized by using this continuous synthesis system weresmaller and more regular shaped than those prepared by conventional synthesis. According to the results, the Cr(VI)residual level increased by increasing the initial Cr(VI) concentration and decreased by increasing the nZVI coatedwith flaxseed glaze (FG-nZVI) dosage. At the Cr(VI) initial concentration of 4mg L1, the Cr(VI) was removed entirelyat almost all dosages of FG-nZVI. Optimal amount of FG-nZVI was 62.73mg L1 when applied at 4mg L1 of Cr(VI)at optimum pH 6.64, resulting in the Cr(VI) residual concentration of 0.05mg L1. The results of saturated porousmedia showed that injection background solutions enhanced the transfer of nanoparticles in the porous medium, resultingin the adequate removal along the desired radius. The results illustrated that using FG-nZVI can be effective forpractical groundwater remediation.

Preparation of Petaloid TPEE@AlOOH Nanofibers with Cr (VI)-Removal Capacity

Jiao-Na Wang,Bin-Bin Jia,Cong-Ju Li 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.2

Hexavalent chromium (Cr (VI)) is a highly toxic pollutant which is harmful to marine organisms as well as humanity. Removing Cr (VI) from water is a hot-spot in environmental remediation. In this work, a novel kind of composite nanofibers membrane (thermal plastic elastomer ester (TPEE)@AlOOH) was first proposed by a simple method, based on a hybrid strategy composed of electrospinning and hydrothermal method. The obtained nanofibrous membrane was turned out to be a petaloid structure, which can enlarge the specific surface area of electrospun fibers. Furthermore, the Cr (VI) removal experiments suggested that the obtained nanofibrous membrane showed a high and fast efficiency, a stable recyclable property for the Cr (VI) removal. Therefore, such a novel nanofibrous membrane can be potentially widely used in Cr (VI) removal.

Fabrication of recyclable UiO-66-NH2/PVDF hybrid fibrous membrane for Cr(VI) removal in wastewater

Fan Yu,Liusha Cen,Caihong Lei,Feichao Zhu,Lan Zhou,Hailin Zhu,Bin Yu 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.123 No.-

Efficient and recyclable water treatment technology plays a vital role in practical application of Cr(Ⅵ)removal. Zr-based metal–organic framework (UiO-66-NH2) is widely used in wastewater treatmentdue to its water stability. Powdery UiO-66-NH2 has disadvantages of easy aggregation, reclamation difficultyand secondary pollution. In this work, UiO-66-NH2 was successfully loaded on electrospunpolyvinylidene fluoride (PVDF) fibers by in-situ growth to achieve efficient adsorption and photoreductionof Cr(Ⅵ). Grooved surface of PVDF fibers and truncated octahedron shape of UiO-66-NH2 ensuredthe loading uniformity and firmness. The loading rate and size of UiO-66-NH2 crystals increased withthe amount of trifluoroacetic acid (TFA) in the preparation process. Meantime, the introduction of TFAin synthesis was conducive to the separation efficiency of photogenerated carries. When the additionamount of TFA was 5 ml, UiO-PVDF-3 with loading rate of 44.8% exhibited best Cr(VI) adsorption andphotocatalysis performance. For the pure adsorption process, the adsorption capacity of UiO-PVDF-3 at90 min was 3.76 mg/cm2, and the corresponding removal rate was 95.8%. When visible light was applied,the Cr(VI) removal rate for UiO-PVDF-3 reached to about 95.0% at 45 min. Furthermore, regenerationexperiments showed UiO-PVDF-3 had excellent adsorption and photocatalysis reusability. Based on thismethod, synthesized UiO-66-NH2/PVDF hybrid membrane as a bifunctional material for adsorption andphotocatalysis realizes the reuse of UiO-66-NH2 crystals conveniently and avoids secondary pollutionduring Cr(VI) wastewater treatment.

순환식 반응기에서 $TiO_{2}$ 광촉매를 이용한 Chromium(VI)의 제거에 미치는 영향인자에 대한 연구

김현용,조일형,이소진,기원주,이홍근,Kim, Hyun-Yong,Cho, Il-Hyoung,Lee, So-Jin,Ki, Won-Ju,Lee, Hong-Keun 한국환경보건학회 1999 한국환경보건학회지 Vol.25 No.3

This study was carried out the removal of Cr(VI) which was known to the toxic pollutant in industry using the process of UV and TiO$_2$ photocatalyst in a circular type reactor. In this experiment, the series of photocatalytic process for the removal of Cr(VI) has been selected as a model reaction in a circular type reactor in order to obtain the basic data on the influence of various experimental parameters such as circulation flow rate, pH of solution, initial Cr(VI) light illumination and TiO$_2$ dosage, and salicylic acid concentration. The results of this study were as follows; 1. With both UV light illumination and TiO$_2$ present, Cr(VI) was more effectively eliminated than with either UV or TiO$_2$ alone. 2. As the circulation flow rate of solution increased, the removal efficiency of Cr(VI) was increased. However, over 2.4 l/min of circulation flow rate, the efficiency wa limited. 3. A increase in the photocatalytic removal of Cr(VI) was noticed with decreasing pH. 4. An increase in the photocatalytic removal of Cr(VI) was noticed with decreasing Initial Cr(VI) concentration and first order kinetics was observed from the result at different initial concentration of Cr(VI). 5. Photocatalytic removal efficiency of Cr(VI) increased with increasing TiO$_2$ dosage. However, over 1.0 g/l of TiO$_2$ dosage, the efficiency reached a plateau. 6. As low concentration of saliculic acid were added, there was an increase in the removal efficiency of Cr(VI). However, over 300 mg/l of salicylic acid, the efficiecy was decreased. It eas found that application of photocatalysis to water treatment that contains both Cr(VI) and salicylic acid was possible.

Synthesis of B4C powder via the carbothermal reduction and photoreduction of Cr(VI) on B4C under visible light irradiation

Koysuren Ozcan,Koysuren Hafize Nagehan 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.5

The environmental problem caused by wastewater containing hexavalent chromium (Cr(VI)) is of great interest and photocatalytic technology has recently been recognized as a suitable method for dealing with wastes containing Cr(VI). In this study, boron carbide (B4C) powders were synthesized through a carbothermal reduction process using a polymer precursor, polyvinyl borate (PVB), and boric acid. The synthesized B4C powders were studied as a photocatalyst for the removal of Cr(VI) from aqueous solutions under visible light irradiation. The effects of the B4C seed crystals and the Ni catalyst on the crystal purity as well as the Cr(VI) photoreduction efficiency of the prepared B4C powders were studied. B4C, synthesized in the presence of both the B4C seed crystals and the Ni catalyst, resulted in improved crystal purity, leading to an enhancement in the Cr(VI) photoreduction efficiency. The highest Cr(VI) removal rate of 65.1% was obtained. While the irradiation distance did not affect the Cr(VI) photoreduction efficiency much, the highest Cr(VI) removal was obtained with the visible light source (141 klux). The Cr(VI) removal rate was increased approximately 1.4 times with B4C powders synthesized in the presence of both the B4C seed crystals and the Ni catalyst. In addition, the effect of various parameters like the intial pH, Cr(VI) concentration and photocatalyst concentration on the Cr(VI) photoreduction efficiency of B4C was examined. Within the scope of examining the recyclability of the prepared photocatalyst, the Cr(VI) removal rate of B4C decreased from 65.1 to 52.4% after four consecutive cycles of Cr(VI) photoreduction experiments.

Scrap iron packed in a Ti mesh cage as a sacrificial anode for electrochemical Cr(VI) reduction to treat electroplating wastewater

Ya, Vinh,Guillou, Esther Le,Chen, Yi-Ming,Yu, Jui-Hsuan,Choo, Kwang-Ho,Chuang, Sheng-Ming,Lee, Shou-Jen,Li, Chi-Wang Elsevier 2018 JOURNAL- TAIWAN INSTITUTE OF CHEMICAL ENGINEERS Vol.87 No.-

<P><B>Abstract</B></P> <P>A novel sacrificial anode comprised of scrap iron packed inside a cage made of titanium mesh was developed for Cr(VI) reduction. With electric currents applied, the surface passivation of scrap iron electrode could be avoided. Due to the large surface area with open structures provided, the applied current densities (1.18–3.54 mA/cm<SUP>2</SUP>) were low, resulting in low operating voltage and energy consumption. Complete Cr(VI) removal was achieved with electric currents applied, whereas only 20% of the Cr(VI) was removed without electricity. Direct Cr(VI) reduction on the iron surface was a dominant mechanism for the system operated at low (0.25 A) or no current. Acidic pH levels were more effective in Cr(VI) removal, due to more adsorption of Cr(VI) onto the precipitated Fe hydroxide. The trend in total Cr removal was almost the same as that of Cr(VI) removal, but time required to complete total Cr removal was extended. With intermittent electricity supply at a high electric current intensity, the energy consumption of the system was more efficient. Using scrap iron as a sacrificial anode under the intermittent current condition can save 72–77% of the total operational costs required by the conventional plate electrode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel anode packed with scrap iron inside a Ti mesh was used for reducing Cr(VI). </LI> <LI> Electroplating wastewater containing Cr(VI) and Ni(II) was treated. </LI> <LI> Current intensity and initial pH affect the Cr(VI) reduction pattern significantly. </LI> <LI> Intermittent but high electric current supply saved 72–77% of the operating costs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Cr(VI) removal from aqueous solution by thermophilic denitrifying bacterium Chelatococcus daeguensis TAD1 in the presence of single and multiple heavy metals

Han Li,Shaobin Huang,Yongqing Zhang 한국미생물학회 2016 The journal of microbiology Vol.54 No.9

Cr(VI) pollution is increasing continuously as a result of ongoing industrialization. In this study, we investigated the thermophilic denitrifying bacterium Chelatococcus daeguensis TAD1, isolated from the biofilm of a biotrickling filter used in nitrogen oxides (NOX) removal, with respect to its ability to remove Cr(VI) from an aqueous solution. TAD1 was capable of reducing Cr(VI) from an initial concentration of 10 mg/L to non-detectable levels over a pH range of 7–9 and at a temperature range of 30–50°C. TAD1 simultaneously removed both Cr(VI) and NO3 −-N at 50°C, when the pH was 7 and the initial Cr(VI) concentration was 15 mg/L. The reduction of Cr(VI) to Cr(III) correlated with the growth metabolic activity of TAD1. The presence of other heavy metals (Cu, Zn, and Ni) inhibited the ability of TAD1 to remove Cr(VI). The metals each individually inhibited Cr(VI) removal, and the extent of inhibition increased in a cooperative manner in the presence of a combination of the metals. The addition of biodegradable cellulose acetate microspheres (an adsorption material) weakened the toxicity of the heavy metals; in their presence, the Cr(VI) removal efficiency returned to a high level. The feasibility and applicability of simultaneous nitrate removal and Cr(VI) reduction by strain TAD1 is promising, and may be an effective biological method for the clean-up of wastewater.

Removal mechanism for chromium (VI) in groundwater with cost-effective iron-air fuel cell electrocoagulation

Ali Maitlo, Hubdar,Kim, Ki-Hyun,Yang Park, Joo,Hwan Kim, Jung Elsevier 2019 Separation and purification technology Vol.213 No.-

<P><B>Abstract</B></P> <P>Metal-air fuel cell electrocoagulation is one of the most cost-effective and innovative treatment options for metals in water. Here, the removal mechanism of chromium (Cr(VI)) was assessed using an iron-air fuel cell electrocoagulation (IAFCEC) system. Simultaneously, the effects of such treatment were also investigated with respect to a list of parameters controlling groundwater quality. During the IAFCEC operation, in-situ production of stable iron hydroxides (e.g., maghemite, hematite, and goethite) was experienced due to the sacrificial oxidation of the iron anode electrode. Therefore, these iron hydroxides were responsible for direct co-precipitation of aqueous Cr(VI). The removal efficiency of the system was assessed by varying the initial concentrations of Cr(VI) such as1, 5, and 10 mg L<SUP>−1</SUP>). The IAFCEC, when operated with low concentrations of competing anions (e.g., silicate, phosphate, magnesium, and calcium), was capable of treating 6 L of water containing 1 mg L<SUP>−1</SUP> Cr(VI) per day with an operating cost of 0.2 USD m<SUP>−3</SUP>. This study demonstrates the IAFCEC as one of the most cost-effective treatment methods for Cr(VI) removal based on evaluation of performance relative to other options commonly available.</P> <P><B>Highlights</B></P> <P> <UL> <LI> IAFCEC is most cost-effective for Cr(VI) treatment and power generation. </LI> <LI> In-situ produced iron hydroxides were used for direct co-precipitation of Cr(VI). </LI> <LI> IAFCEC can obtain 100% Cr(VI) removal within 4 h with operating cost of 0.2 USD m<SUP>3</SUP>. </LI> <LI> Merits of system are evident as it is less dependent upon operating parameters. </LI> </UL> </P>

Detailed investigation of effective trace Cr(VI) removal mechanism by anion exchange resin with phenol–formaldehyde matrix

Renuka Verma,Pradip K. Maji,Sudipta Sarkar 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.111 No.-

Prolonged exposure to trace Cr(VI) concentrations in potable water can cause serious health problems inliving beings. A weak base anion exchange resin, Duolite A7, showed a large capacity for trace Cr(VI)removal from a background of competing anions present at much higher concentrations, while conventionalion exchangers and adsorbents become ineffective due to lack of selectivity under similar conditions. The objective of this study was to find out the mechanism behind such significant capacityshown by the resin. Fixed-bed column studies showed that the resin was fully exhausted below 4,000bed volumes (BVs) for pH 7, whereas no breakthrough was observed for 25,000 and 131,000 BVs at pH5 and 3, respectively. Extensive characterization studies revealed that redox reactions were also occurringinside the resin in addition to ion exchange, where Cr(VI) oxidized the amine functional groupsand phenol–formaldehyde matrix while itself getting reduced to Cr(III). Cr(III) formed was either precipitatedinside the resin as Cr(OH)3 or bound with the oxidation products such as carboxylic acid groups. Analysis of treated water showed that formaldehyde, a carcinogen, was formed due to oxidative attackof Cr(VI) on the resin and was released in the effluent at trace concentrations. A detailed understandingof the mechanism would motivate the development of such redox-active sorbents for selective trace Cr(VI) removal from contaminated drinking water.