Green-synthesized, biochar-supported nZVI from mango kernel residue for aqueous hexavalent chromium removal: Performance, mechanism and regeneration

A biochar-supported green nZVI(G-nZVI@MKB)composite was synthesized using mango kernel waste with“dual identity”as reductant and biomass of biochar.The G-nZVI@MKB with a Fe/C mass ratio of 2.0(G-nZVI@MKB2)was determined as the most favorable composite for hexavalent chromium(Cr(VI))removal.Distinct influencing parameters were discussed,and 99.0%of Cr(VI)removal occurred within 360 min under these optimized parameters.Pseudo-second order kinetic model and intra-particle diffusion model well depicted Cr(VI)removal process.The XRD,FTIR,SEM,and XPS analyses verified the key roles of G-nZVI and functional groups,as well as the primary removal mechanisms involving electrostatic attraction,reduction,and complexation.G-nZVI@MKB2 exhibited good stability and reusability with only a 16.4%decline in Cr(VI)removal after five cycles.This study offered evidence that mango kernel could be recycled as a beneficial resource to synthesize green nZVI-loaded biochar composite for efficient Cr(VI)elimination from water.

Solidification/Stabilization of Chromium in Red Mud-based Geopolymer

Up to 1.5wt%of Cr(Ⅲ)salts(CrCl_(3),and Cr_(2)O_(3))and Cr(Ⅵ)salts(Na_(2)CrO_(4),and CaCr_(2)O_(7))were incorporated into red mud-based geopolymers,respectively.The solidification/stabilization,compressive strength,and durability of the Cr-containing geopolymers were investigated.The experimental results indicate that the red mud-based geopolymer could effectively solidify/stabilize different types of Cr salts with solidification/stabilization rates of above 99.61%.Geopolymers are environmentally safe when the dosage of CaCr_(2)O_(7)is≤1.0wt%,or the dosage of CrCl_(3),Cr_(2)O_(3),and Na_(2)CrO_(4)is≤1.5wt%,respectively.The effects of Cr salts on the compressive strength varies with the type and content of Cr salts.The freeze-thaw cycle is more destructive to geopolymer properties than sulfate attack or acid rain erosion.The solidification/stabilization of Cr is mainly attributed to the following reasons:a)The chemical binding of Cr is related to the formation of Cr-containing hydrates(eg,magnesiochromite((Mg,Fe)(Cr,Al)_(2)O_(4)))and doping into N-A-S-H gel and C-A-S-H gel framework;b)The physical effect is related to the encapsulation by the hydration products(e g,N-A-S-H gel and C-A-S-H gel).This study provides a reference for the treatment of hazardous Cr-containing wastes by solid waste-based geopolymers.

Effective Elimination of Hazardous Chromium (VI) Using Periodic Elements and Contemporary Adsorption Methods by Using Magnesium Ferrite Nanoparticle: A Review

A well-known hazardous metal and top contaminant in wastewater is hexavalent chromium. The two forms of most commonly found chromium are chromate ( CrO 4 2− ) and dichromate ( Cr 2 O 7 2− ). Leather tanning, cooling tower blow-down, plating, electroplating, rinse water sources, anodizing baths etc. are the main sources of Cr (VI) contamination. The Cr (VI) is not only non-biodegradable in the environment but also carcinogenic to living population. It is still difficult to treat Cr contaminated waste water effectively, safely, eco-friendly, and economically. As a result, many techniques have been used to treat Cr (VI)-polluted wastewater, including adsorption, chemical precipitation, coagulation, ion-exchange, and filtration. Among these practices, the most practical method is adsorption for the removal of Cr (VI) from aqueous solutions, which has gained widespread acceptance due to the ease of use and affordability of the equipment and adsorbent. It has been revealed that Fe-based adsorbents’ oxides and hydroxides have high adsorptive potential to lower Cr (VI) content below the advised threshold. Fe-based adsorbents were also discovered to be relatively cheap and toxic-free in Cr (VI) treatment. Fe-based adsorbents are commonly utilized in industry. It has been discovered that nanoparticles of Fe-, Ti-, and Cu-based adsorbents have a better capacity to remove Cr (VI). Cr (VI) was effectively removed from contaminated water using mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.). Initial findings suggest that Cr (VI) removal from wastewater may be accomplished by using magnesium ferrite nanomaterials as an efficient adsorbent.

Investigation of Hexavalent Chromium Reduction in Strong Saline and Acidic Nitro-Phosphate Solutions

Phosphorus fertilizers from less pure sedimentary sources become increasingly important, due to depletion of phosphorus from igneous rock of high quality. Consequently, robust methods with potential to remove various types of hazardous elements are required. Among such impurities, hexavalent chromium (Cr(VI)) is very likely to become a future challenge. Different industrial ways to treat phosphate rock are currently being practised, and we have here studied how chromium behaves when using the nitro-phosphate process. The reduction mechanism of Cr (VI) in nitric acid and phosphoric acid solutions was investigated by measuring redox potential and UV-VIS spectra. The results show that Cr (VI) is not stable in strong nitric acid solutions. Reduction of Cr (VI) species decreased with decreasing temperature, NO2 concentration, ionic strength and absence of light. These findings support the proposed reduction reaction:The reduction rate was observed proportional to the nitric acid decomposition: .

Hexavalent Chromium Cr (VI) Removal from Water by Mango Kernel Powder

Metal trace elements (MTE) are among the most harmful micropollutants of natural waters. Eliminating them helps improve the quality and safety of drinking water and protect human health. In this work, we used mango kernel powder (MKP) as bioadsorbent material for removal of Cr (VI) from water. Uv-visible spectroscopy was used to monitor and quantify Cr (VI) during processing using the Beer-Lambert formula. Some parameters such as pH, mango powder, mass and contact time were optimized to determine adsorption capacity and chromium removal rate. Adsorption kinetics, equilibrium, isotherms and thermodynamic parameters such as ΔG˚, ΔH˚, and ΔS˚, as well as FTIR were studied to better understand the Cr (VI) removal process by MKP. The adsorption capacity reached 94.87 mg/g, for an optimal contact time of 30 min at 298 K. The obtained results are in accordance with a pseudo-second order Freundlich adsorption isotherm model. Finally FTIR was used to monitor the evolution of absorption bands, while Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to evaluate surface properties and morphology of the adsorbent.

Corrosion Mechanism of Alumina-magnesia Dry Materials for Smelting Manganese/chromium Steel in Coreless Medium Frequency Induction Furnaces

Alumina-magnesia dry materials are widely used in induction furnace linings, but they show different kinds of damage when melting different kinds of alloy steel. In this paper, the chemical composition, phase composition, and microstructure of the post-use dry materials for the working liners melting different kinds of steel were evaluated. Furthermore, the corrosion mechanism of the steel on the furnace lining materials was comprehensively analyzed. The findings reveal a significant ability of the Mn element in the molten steel to diffuse and penetrate into the refractories. Mn oxidizes to form MnO at the steel-refractory interface, and then forms a liquid phase with Al_(2)O_(3). The Cr element is dissolved into corundum and spinel of the refractories, resulting in lattice defects and structural damage of the materials. TiO2reacts with Al_(2)O_(3) to form Al_(2)TiO_(5), which plays a crucial role in preventing crack formation and propagation. Part of Ti4+dissolves into magnesia-alumina(MA), densifying the materials. TiO2also slows down the reaction between the Cr element and refractory components, further improving the corrosion resistance of the materials.

Reactions of Chromium during the Calcination of Cement Clinker Produced Using Steel Slag

We investigated the effects of calcination temperature(950-1450℃),steel slag content,and the total chromium content of steel slag on the Cr^(6+)contents of clinker samples produced using steel slags with different chromium contents.Additionally,the reactions of chromium in clinker(produced using steel slag)during calcination were studied.It is found that Cr^(6+)conversion increases with increasing calcination temperature to 1250℃,reaching a maximum of 43%-79%,before decreasing to 18%-42%at 1450℃.Cr^(6+)is mainly formed by the oxidation of trivalent chromium(Cr^(3+))during the solid-phase reaction stage of clinker calcination.Furthermore,the Cr^(6+)content of a clinker sample is proportional to the chromium content of its raw meal precursor and is mainly in the form of water-insoluble calcium chromate(CaCrO_(4)).The chromium in clinker is mainly distributed in tricalcium aluminate and tetracalcium aluminoferrite,however,some is present in silicate minerals.We expect to inform the monitoring and control of the Cr^(6+)content of clinker(produced using steel slag)and resulting cement.

Synthesizing and characterizing the magnetic EDTA/chitosan/CeZnO nanocomposite for simultaneous treating of chromium and phenol in an aqueous solution

A new magnetic nanocomposite chitosan/EDTA/CeZnO(MEC-CeZnO)is synthesized as an efficient and eco-friendly bio-compound for the removal of chromium Cr(VI)metal ions and phenol organic matters from aqueous solutions.Nanocomposites are characterized using field emission scanning electron microscope,energy dispersive X-ray spectroscopy,transmission electron microscope,X-ray diffraction,X-ray photoelectron spectroscopy,Fourier transform infrared spectroscopy,diffuse reflection spectroscopy,and PL methods.The reduction rate of Cr(VI)ions and phenol degradation is evaluated under various experimental conditions,separately and simultaneously.The average pore diameter and specific surface of MEC-CeZnO nanocomposite are obtained 50 nm and 210 m^(2)·g^(-1)respectively,which suggest the successful synthesis of the nanocomposite because of the increased surface area and reduced pores in comparison to previous studies.Moreover,the best Cr(VI)and phenol reduction efficiencies are 98%and 92%at 180 min of retention time,both following the Langmuir-Hinshelwood first-order kinetics.The mechanisms of Cr(VI)and phenol removal from aqueous solutions involved Cr(VI)reduction,phenol oxidation,and adsorption.Examining the reusability of MEC-CeZnO showed that both degradation and recovery capacity is stable in 5 cycles.

Facile synthesis of chromium chloride/poly(methyl methacrylate) core/shell nanocapsules by inverse miniemulsion evaporation method and application as delayed crosslinker in secondary oil recovery

Cr(III)ehydrolyzed polyacrylamide(HPAM)gels have been extensively studied as a promising strategy controlling waste water production for mature oilfields.However,the gelation time of the current technologies is not long enough for in-depth placement.In this study,we report a novel synthesis method to obtain chromium chloride/poly(methyl methacrylate)(PMMA)nanocapsules which can significantly delay the gelation of HPAM through encapsulating the chromium chloride crosslinker.The chromium chloride-loaded nanocapsules(CreNC)are prepared via a facile inverse miniemulsion evaporation method during which the hydrophobic PMMA polymers,pre-dispersed in an organic solvent,were carefully controlled to precipitate onto stable aqueous miniemulsion droplets.The stable aqueous nanodroplets(W)containing Cr(III)are dispersed in a mixture of organic solvent(O1)with PMMA and nonsolvent medium(O2)to prepare an inverse miniemulsion.With the evaporation of the O1,PMMA forms CreNCs around the aqueous droplets.The CreNCs are readily transferred into water from the organic nonsolvent phase.The CreNCs exhibit the tunable size(358-983 nm),Cr loading(7.1%-19.1%),and Cr entrapment efficiency(11.7%-80.2%),with tunable zeta potentials in different PVA solutions.The CreNCs can delay release of Cr(III)and prolong the gelation time of HPAM up to 27 days.

Interface characteristics and wear resistance of Ni-B_(4)C plated ZTA reinforced high chromium cast iron composite

A chemical composite plating of Ni-B_(4)C was used to prepare the surface-modified zirconia toughened alumina(ZTA)ceramic particles.The ceramic preforms were prepared by the plated ZTA and sodium silicate solution binder,followed by casting infiltration to prepare the ZTA particles reinforced high chromium cast iron(HCCI)composites.The result reveals that a distinct interface layer forms at the ZTA/HCCI interface,which consists of phases of ZrB_(2),FeB,Fe_(2)B,and NaSiO_(4).The interfacial wettability between ZTA and HCCI is improved by the diffusion and reaction of Ni and B_(4)C.The wear test reveals that the Ni-B_(4)C plated ZTA particles can effectively improve the wear resistance of the ZTA/HCCI composite,and the wear rate of the composite is decreased to 11.6%of HCCI.

Finite Element Analysis of Large Size Chromium Oxide Green Bodies During Firing

To prevent dense chromium oxide covers from cracking during firing,such as internal cracking,surface cracking and fracture,the firing process of dense chromium oxide products was simulated,and the performance parameters at several specific temperatures before and after densification of chromium oxide green bodies were tested.The temperature difference and the stress difference of chromium oxide green bodies were calculated by Finite Element Software at heating and cooling rates of 10,20,30 and 40℃·h^(-1),respectively.The results show that large temperature difference and thermal stress difference are the main causes of internal cracking,surface cracking and fracture of the brick.Suitable heating rates reduce or avoid internal cracking of the brick.When the heating rate is 30℃·h^(-1) below 1450℃and 10℃·h^(-1) above 1450℃,the temperature difference and the thermal stress difference in the brick are below 4℃and 4 MPa,respectively,and there is no internal crack in the brick after firing.The initial cooling stage is the key stage that causes cracking or fracture of bricks.When the cooling rate is 20℃·h^(-1) above 1450℃,the thermal stress difference in the brick is less than 4 MPa,which can significantly reduce the surface cracks and fracture of the brick.

某铬渣堆污染地下水六价铬污染特征与迁移转化规律研究

我国铬渣堆历史存量较大,渣堆渗滤液中的六价铬[Cr(Ⅵ)]毒性大、迁移性强。为探究污染源特征、场地水文地质条件和水文地球化学过程综合作用下Cr(Ⅵ)在地下水中的迁移转化规律,文章以某铬污染场地为例,通过水样采集与分析,利用克里格插值、因子分析、水化学计算、Piper三线图和离子比等方法查明地下水中Cr(Ⅵ)的空间分布与水化学特征,识别水体中Cr(Ⅵ)的主要赋存形式,并探讨影响Cr(Ⅵ)在地下水中迁移转化的主控因素。结果表明:(1)场地40 m以浅的2个含水层均受到了Cr(Ⅵ)污染,污染范围和程度差异显著。(2)Cr(Ⅵ)在地下水中主要以和Cr_(2)O_(2)-7 HCO_(3)^(-) SO_(4)^(2-)2种形式存在,浓度极低,高浓度Cr(Ⅵ)水点的阴离子以和为主,阳离子以Na^(+)和Ca^(2+)为主。(3)降水淋滤SO_(4)^(2-) HCO_(3)^(-)和渗漏导致含有大量Na+、和Cr(Ⅵ)的渗滤液进入地下水,使地下水pH值升高;高浓度的和弱氧化环境下铁氧化物的溶解可以促进Cr(Ⅵ)在地下水中的迁移;锰氧化物和有机质通过氧化还原反应改变地下水中Cr(Ⅵ)浓度;浅层地下水的蒸发浓缩作用加剧Cr(Ⅵ)在地下水中的富集。研究成果可为铬渣类污染场地的风险管控与后期修复提供有力支撑。

Impact of Chromium Propionate Supplementation and Days of Adaptation on Energy Status in Newly Weaned Steer Calves*

The objective of this research was to evaluate the influences that supplemental dietary chromium propionate (CrP;0 or 0.4 mg·kg-1 added to the total diet on a DM basis) has on plasma indicators of energy status in newly weaned steers upon introduction to the feedlot. For this experiment single source, Angus steers (n = 28;BW = 289 ± 12.0 kg) from a ranch in Western South Dakota were weaned and immediately shipped 579 km to the Ruminant Nutrition Center (RNC) in Brookings, SD. Steers were allotted to one of four 7.6 m × 7.6 m pens (2 pens/diet;7 steers/pen) at 4 d post-arrival to the RNC and test diets were initiated. No anabolic implant was used in this study. Subsequent BW measurements were obtained at 1400 h, to accommodate a post-prandial timing for blood sampling. This was 4 h after initial access to feed, and immediately prior to the afternoon feed delivery. Weights and blood sampling occurred on d 5, 12, 19, and 33. Whole blood samples were collected from all steers via jugular venipuncture and separated as plasma. There were no diet x day interactions (P ≥ 0.51) for plasma glucose, insulin, or urea-N. Plasma glucose, insulin, and urea-n levels were similar between diets (P ≥ 0.35). Plasma glucose and urea-n levels were not different across days (P ≥ 0.59). Insulin levels differed as a result of days of adaptation and were greatest (P = 0.01) on d 12 regardless of diet. There tended (P = 0.12) to be a diet x day interaction for NEFA levels. Plasma NEFA levels tended to be lower (P = 0.13) for calves fed CrP on d 5, and were greater (P = 0.09) on d 12 in calves fed CrP. The shift in NEFA on d 12 coincided with the spike in insulin levels. Both events occurred at the time that NEg intake was approaching the acclimated plateau and neither event impacted glucose status. In non-ruminants, elevated insulin concentrations decrease circulating NEFA levels. We detected minimal differences in regard to plasma indicators of lipid metabolism in this study due to chromium supplementation. These data indicate that ruminants may differ from non-ruminants in the regulation and maintenance of glucose status and body fat catabolism during the post-absorptive state.

陕北靖边高铬地下水中硝酸根分布及来源

天然高铬地下水通常含有较高浓度的硝酸根,然而高铬地下水中硝酸根来源及其联系却并不清楚。本文以陕北黄土高原靖边西南地区的高铬地下水为研究对象,采集了不同深度的地下水和沉积物样品,并测试了地下水样品中的溶解Cr、主要阴阳离子、δ^(18)O、δD、δ^(18)O-NO_(3)、δ^(15)N-NO_(3)等以及沉积物的主要组分和可溶性组分。研究结果表明,研究区地下水的水化学组分主要受水文地质条件的影响。第四系黄土潜水水化学类型主要为HCO_(3)-Na型和HCO_(3)-Ca-Mg型;白垩系环河组、洛河组砂岩承压水水化学类型复杂,主要为HCO_(3)-SO_(4)-Cl-Na-Mg型、HCO_(3)-SO_(4)-Na-Mg型、SO_(4)-Cl-Na-Mg型,地下水处于偏碱性、氧化的环境,具有较高的可溶盐含量。潜水的水化学组分主要来自含水层中硅酸盐风化;承压水水化学组分主要来源于蒸发盐的溶解。垂向上,承压水中硝酸根的平均浓度高于潜水和地表水;地下水硝酸根浓度超标率在研究区从东北到西南呈现高-低-高的趋势;沉积物中可溶性硝酸根与地下水样品在深度上具有相似的变化规律,表明地下水硝酸根主要来源于沉积物。δ^(18)O-NO_(3)和δ^(15)N-NO_(3)结果表明,硝化反应是研究区氮素循环转化的主要过程。在偏碱性氧化性地下水环境中,受溶解氧、硝酸根和硝化反应等多种因素的共同作用,铬趋于从岩石中氧化溶解,迁移进入地下水中。

六价铬对红芸豆种子萌发和幼苗生长的毒害作用及外源NO的缓解效应

为了研究铬(Cr)对红芸豆种子萌发和早期幼苗生长的胁迫作用及硝普钠(SNP,NO供体)的缓解作用,以红芸豆品种‘红芸3号’为试材,采用纸间发芽方法和水培法,研究Cr和外源NO对红芸豆种子萌发、种胚和幼苗抗氧化系统、幼苗光合特性以及营养元素吸收转运的影响。结果表明,20μmol·L^(−1)K_(2)Cr_(2)O_(7)胁迫诱发红芸豆种胚和幼苗氧化损伤,抑制幼苗对营养元素的吸收和转运,降低幼苗光合作用,进而抑制红芸豆种子萌发和早期幼苗的生长。添加100μmol·L^(−1)SNP(外源NO)可减轻Cr对种胚和幼苗的氧化胁迫伤害,降低Cr在幼苗中的积累,促进幼苗对营养元素的吸收和转运,增强幼苗光合作用。种子萌发生长72 h时,20μmol·L^(−1)K_(2)Cr_(2)O_(7)胁迫下添加SNP,种胚H_(2)O_(2)、O_(2)^(-)和MDA含量分别比Cr胁迫处理降低36.15%、30.96%和34.97%;Cr胁迫下,添加SNP幼苗生长10 d,根系H_(2)O_(2)、O_(2)^(-)和MDA含量分别比Cr胁迫处理降低55.25%、48.60%和33.54%,叶片H_(2)O_(2)、O_(2)^(-)和MDA含量分别比Cr胁迫处理降低27.71%、36.40%和53.85%,根系活力比Cr胁迫处理升高59.16%;幼苗根和叶中Cr含量比Cr胁迫处理降低69.14%和24.08%,幼苗根中Mg、Fe、Cu和Zn含量比Cr胁迫处理分别增加37.10%、17.96%、5.17%和13.60%,幼苗叶中Mg、Fe、Cu、Zn元素含量比Cr胁迫处理分别增加32.57%、29.49%、22.45%和36.07%;幼苗净光合速率和PSⅡ最大光合效率比Cr胁迫处理提高58.60%和11.27%。外源NO通过诱导种胚抗氧化酶活性提高,降低幼苗对Cr的吸收,促进幼苗对营养元素的吸收和转运,增强幼苗光合作用,缓解Cr对红芸豆种子萌发和早期幼苗生长的胁迫作用。

生物淋滤电动修复湖泊底泥中的铬

该文采用生物淋滤电动复合技术修复底泥,经生物淋滤后底泥中铬形态发生了改变,可交换离子态、碳酸盐结合态的铬含量比例明显增加,而铁锰氧化物结合态、硫化物及有机结合态以及残渣态的比例含量明显下降(可为电动修复底泥时铬的迁移提供有利条件)。单纯电动修复铬的去除率为32.6%,单纯生物淋滤铬的去除率为25.1%,淋滤去除率与底泥的pH值和氧化还原电位紧密相关。经生物淋滤电动复合处理后,铬的去除总量可达53.4%。生物淋滤电动复合技术对可交换的离子态、碳酸盐结合态、硫化物及有机结合态的铬去除率较高,特别是对碳酸盐结合态的铬去除率达到61.1%。实验表明电动生物淋滤技术具有协同作用,适合湖泊底泥铬污染治理。

不同材料复合添加对土壤铬形态的影响

以铬污染黄壤为研究对象,选择有机材料(泥炭)、pH值调节剂(沸石)、生物炭(鸡粪)3种不同种类的土壤重金属污染改良剂,采用正交试验L_(9)(3^(4))设计和室内盆栽试验,考察不同复合材料组对土壤中重金属铬形态、pH值、有机质含量的影响。结果表明:沸石的添加提高了土壤pH值、有机质含量,增加了土壤可还原态、可氧化态铬含量;鸡粪的添加通过提高土壤pH值从而增加土壤可还原态铬的含量;泥炭的添加提高了土壤有机质含量、土壤可氧化态铬含量,降低了土壤可交换态铬含量。

改性钨酸铋纳米材料用于六价铬与环丙沙星光催化共降解研究

抗生素与重金属离子常在废水中共存,提高了废水处理难度,因此亟需高效的处理方法实现二者的共降解.在此,通过一种简单的溶剂热法合成了具有氧空位和3D中空结构钨酸铋光催化材料,实现了六价铬和环丙沙星的高效光催化共降解,光催化反应40 min后可将二者降解99%.实验及表征结果表明,氧空位的引入促进了光生载流子的分离与迁移,使得更多的电子和空穴参与氧化还原反应,进而显著提高了光催化共降解效率.同时,结合降解转化产物检测结果,分析了降解机理与路径.本工作为抗生素/重金属共存废水的处理提出了一种可行的高效方法.

电动法去除污染土中重金属铬的试验研究

针对土壤铬污染严重的问题,通过自行设置的电动去除装置,研究电动法在不同电压、电解液种类和浓度的条件下对铬去除效果的影响。结果显示:电动法能够有效去除土壤中的重金属铬,并且土壤中铬(Ⅵ)的迁移受电压的影响较大,当电压从10 V增大至40 V时,铬(Ⅵ)的去除率提高了12.25百分点。电解液中加入0.05 mol/L十二烷基苯磺酸钠(Sodium Dodecyl Benzene Sulfonate, SDBS)后铬(总)的去除率提高了5.94百分点,但增大SDBS浓度对提升铬的去除率没有明显效果。柠檬酸(Citric Acid, CA)可显著促进铬的迁移,柠檬酸浓度越大,铬的去除效率越高。在电解液中加入0.15 mol/L柠檬酸后铬(总)的去除率增长幅度达到最大,提高了18.03百分点,铬(Ⅵ)的去除率达到了93.4%,铬(总)的去除率达到了74.96%。其中,弱酸提取态和可还原态铬的去除量占铬(总)去除量的95%左右,CA能够促进残渣态铬向弱酸提取态转换并促进铬的迁移,使各形态铬的残余量均有所下降,进而使铬污染土壤的毒性大幅降低。经电动去除后,土壤表面呈现出针状、絮状或颗粒状,并出现了大量细小的孔隙,结构变得相对松散。

综合法二氧化氯生产系统废水除铬实例

以某浆纸厂含铬废水处理工程实例为研究对象,针对综合利用自产化学药品和现有设备开发的间歇性六价铬(Cr^(6+))综合处理系统,探讨了二氧化氯车间Cr^(6+)废水产生原因及性质,根据不同的反应池pH值、反应温度、反应时间和硫磺投加量对废水中Cr^(6+)还原效果的影响,确定了二氧化硫还原法去除Cr^(6+)的最佳反应条件,并结合实际生产数据,展示了Cr^(6+)还原效果。结果表明,有效去除高浓度含铬废水中Cr^(6+)的条件为:pH值=2~4、反应温度控制在40~60℃、硫磺投加量为理论反应所需投加量的1.4~1.6倍、反应时间40 min。3次二氧化氯车间停修废水出水中Cr^(6+)含量均低于0.005 mg/L,总铬含量均低于0.06 mg/L,符合《污水综合排放标准》(GB 8978—1996)中的要求,证实了间歇性Cr^(6+)综合处理系统处理的有效性。