Bi₂WO₆ was synthesized by adopting hydrothermal method, and a composite photocatalyst of Ag-AgI/Bi₂WO₆ was then prepared by photoinduction with Bi₂WO₆ as the carrier for AgI. The prepared photocatalyst samples were characterized by X-ray diffraction, scanning electron microscope and selected area electron diffraction analysis. After that, the rhodamine B (RhB) was degraded by photocatalysis, and the photocatalytic performance of Ag-AgI/Bi₂WO₆ was also studied. The results show that photocatalyst of Ag-AgI/Bi₂WO₆ can lead to a better degradation of RhB, with the degree of degradation up to 99.8%, which remains to be 95.5% after the photocatalyst has reused for five times. The photocatalytic degradation and repeatability tests results show that the composite photocatalyst of Ag-AgI/Bi₂WO₆ exhibits both better photocatalytic activity and better stability, compared with the pure Bi₂WO₆.

A self-supporting adsorbent (MF@MIL-53(Fe)) was prepared by in-situ growth of MIL-53(Fe) on melamine sponge (MF), and was applied to the adsorption of Cr(Ⅵ) in wastewater. It is found that under appropriate conditions, including 0.2 g/L adsorbent, pH of 7, an initial Cr(Ⅵ) concentration of 8 mg/L, the maximum adsorption capacity is 38.9 mg/g after the Cr(Ⅵ) in the wastewater has been adsorbed with MF@MIL-53(Fe) for 120 min. Furthermore, after 5 adsorption/desorption cycles, the maximum adsorption capacity still remains over 90%, showing the adsorbent of MF@MIL-53(Fe) possesses a good recyclability.

According to the quality of the wastewater from the concentrator of a lead-zinc mine in Inner Mongolia, sodium sulfide was used to treat this wastewater. The influence of the dosage and the adding spot of sodium sulfide on the concentrate grade and recovery by recycling such wastewater into Pb-Zn flotation process was evaluated. When COD_Cr and BOD₅ in the wastewater exceed 92.10 and 18.54 mg/L respectively, the recycled wastewater has a great impact on the flotation effect. By adding 1.5 kg/t sodium sulfide into the wastewater before its recycling, the mutual inclusion of lead and zinc in the flotation concentrates can be effectively reduced, but no impact is brought to the grade and recovery of Pb-Zn concentrate. The finally obtained lead concentrate can approach 57.52% Pb grade at 84.72% recovery, while the zinc content therein is reduced to 3.67%.

Solanum nigrum and calendula officinalis were  planted at room temperature in potting soil with different concentration of cadmium, for exploring the cadmium tolerance of these two plants and the variation of accumulation coefficient and translocation factor of cadmium. The results show that both solanum nigrum and calendula officinalis are tolerant to cadmium. In addition, cadmium can promote the growth and development of solanum nigrum and calendula to some extent, enhancing the plant height and biomass production. It is shown that both solanum nigrum and calendula officinalis are plants with high cadmium accumulation, with the accumulation coefficient of cadmium in both shoots and roots exceeding 1. As the cadmium concentration in the potting soil increases, the translocation factor of cadmium in solanum nigrum shows a decrease after an initial increase, with a maximal factor of 3.98, while the translocation factor of cadmium in the calendula officinalis decreases significantly.

Magnetic activated carbon (MAC) was prepared by loading Fe₃O₄ on activated carbon using coprecipitation method, thus the problem in the separation-recovery with commonly-used activated carbon can be solved. When using MAC to adsorb butyl xanthate in mineral processing wastewater, the effects of adsorption time, adsorbent dosage and pH on its adsorption performance were investigated. The results show that under the conditions of pH=7, adsorption time of 3 h, butyl xanthate concentration of 100 mg/L and MAC dosage of 0.6 g/L, the removal rate of butyl xanthate can reach 99.73%. In addition, the adsorption of butyl xanthate conforms well with the second-order kinetic equation and Langmuir isothermal model. MAC has  proven to be an economical and environmentally friendly adsorbent, as 98% MAC can be reclaimed by using magnetic force and the butyl xanthate removal rate remains 76.59% after 5 times of repeated use.

Nanometer zero-valent iron (nZVI) prepared by liquid phase reduction method was used to adsorb Sb(Ⅲ) in wastewater. Then, the obtained nZVI/Sb particles were subjected to calcination at 500 ℃ in an oxygen oven for 8 h, yielding a material of Fe₃O₄/Sb₂O₄. After that, the material was calcinated at 600 ℃ under nitrogen flow with glucose as carbon source, and the Fe₃O₄/Sb₂O₄@C composite powders were finally synthesized. Based on the study of its properties, it is found that the Sb(Ⅲ) in the wastewater with an initial concentration of 100 mg/L is appropriately adsorbed with nZVI by adding an amount of 1.2 g/L at the room temperature for 50 min, leading to the removal rate of Sb(Ⅲ)  up to 73%.   After the incorporation of Sb₂O₄, the prepared iron-base anode has an initial discharge specific  capacity  up to 1065.6 mAh/g. After being coated with carbon layer, the Fe₃O₄/Sb₂O₄@C composite have an obviously improved electrochemical performance, which can remain an discharge specific  capacity of  483.7 mAh/g after 150 cycles at 100 mA/g, and 118.2 mA/g at  2000 mAh/g.

After two materials of fly ash and diatomite were subjected to roasting process for modification, a kind of adsorbent, fly ash-diatomite composite, was prepared and then was used to adsorb Cr(Ⅵ) in mineral processing wastewater. The effects of factors, such as initial concentration of Cr(Ⅵ), pH value, absorbent dosage, temperature and time of adsorption, on the adsorption of Cr(Ⅵ) were investigated. Results show that after roasting and modification, the composite has more porosity and larger specific surface area. The adsorption of Cr(Ⅵ) by the prepared composite is a spontaneous endothermic reaction, predominated by physical adsorption. In the experiment, the composite was prepared by roasting at 500 ℃, and then 20 g/L of such composite was used to adsorb Cr(Ⅵ) from the solution with an initial concentration of Cr(Ⅵ) of 10 mg/L and pH of 2 at a temperature of 60 ℃. After 6 h adsorption, the removal rate of Cr(Ⅵ) from the wastewater reached 70.6%.

For the copper-containing acidic wastewater generated during underground mining process of a copper mine, a new processing technique consisting of copper recovery by replacement with iron filings, neutralization of alkaline tailings overflow, and treatment of coagulation and sedimentation was studied, and the effects of adding amount of iron filings, replacement reaction time and stirring speed on copper replacement rate were all investigated. And then, experiments on the proportion of required alkaline tailings overflow for neutralization of acidic wastewater and on toxicity characteristic leaching of neutralized sludge were performed, as well as the kinetics of replacement process was also studied. The results show that this new processing technique can produce sponge copper grading 35.6% Cu at 92.7% recovery, and the acidic wastewater after treatment can be up to the standard and directly discharged, with the cost of treatment agent at 0.95 yuan/t. Due to no hazardous waste generated, this processing technique can bring remarkable economic and environmental benefits.

A process consisting of flocculation-sedimentation and chemical decalcification was adopted to treat mineral processing wastewater of a tungsten polymetallic ore with high suspended solid (SS) and Ca²⁺ contents. The influence of flocculant dosage, stirring time, stirring speed, water temperature and pH value on flocculation-sedimentation performance was investigated, and the process was then optimized. A closed-circuit test of fluorite flotation with the recycled water shows that the flotation index obtained is similar to that using fresh water, indicating that the wastewater after treatment is applicable for fluorite flotation.

A complex precipitation method was adopted to synthesize CuO nanoparticles, and its morphology and structure were characterized. Then, the CuO nanoparticles were taken as the activator in the degradation of ofloxacin with persulfate. Based on the advanced technology of activated persulfate oxidation, the influences of different parameters, including concentration of K₂S₂O₈ and an initial pH of the ofloxacin solution, on the degradation activity of ofloxacin in the wastewater were investigated. It is found that the degradation rate can reach 95.6% with 10 mg/L of ofloxacin in the wastewater with an initial pH of 3.5, by adding 0.003 0 g/L CuO and 1.0 mmol/L K₂S₂O₈. The experiments on capturing free radicals show that SO₄^-· and O₂^-· are active species for the catalytic degradation of ofloxacin, which is possibly the catalytic reaction mechanism.

A technique featuring separated treatment and recycling was introduced to process a mineral processing wastewater from a tungsten-copper ore concentrator. The wastewater from copper tailings precipitation and copper concentrate filtration is recycled for copper flotation, while the water from tungsten concentrate filtration is returned to the cleaning stage in tungsten flotation. They all can meet the water quality requirement in beneficiation. Tungsten tailings water can be reused in grinding and tungsten flotation after intensified treatment by lime flocculation and Fenton oxidation processes. In a close-circuit test, each type of wastewater from different beneficiation processes was separately returned to the corresponding stages based on its quality, and the obtained technical indicators were equivalent to those from the tests with fresh water.

Natural chalcopyrite (CuFeS₂) was used as a catalyst to activate persulfate (PS) for butyl xanthate wastewater treatment. The influences of CuFeS₂ dosage, PS dosage and initial pH of solution on the removal rate of butyl xanthate in CuFeS₂/PS system were investigated, and the recyclability of CuFeS₂ was also evaluated. The results show that CuFeS₂ can significantly activate PS. After 10 min reaction with initial pH of 3, CuFeS₂ dosage of 4 g/L and PS dosage of 5 mmol/L, the removal rate of butyl xanthate reached 99.23%, while the removal rate of total organic carbon (TOC) was only 31.29%. After the reaction time was extended to 60 min, the TOC removal rate reached 68.31%, and CuFeS₂ still sustained good catalytic activity after being recycled for five times. The UV-Visible absorption spectra of butyl xanthate wastewater degradation showed that butyl xanthate was initially oxidized to alcohols, then decomposed and mineralized to carbon dioxide and water. X-ray diffraction and fourier transform infra-red spectroscopy analysis showed that CuFeS₂ reacted with PS without surface passivation, thus could be reused. A free radical quenching test and an electron spin resonance analysis showed that the removal mechanism of xanthate included free radical degradation and CuFeS₂ physisorption, in which sulfate radical (SO₄^-·) and hydroxyl radical (HO·) were the main active substances to promote xanthate degradation, and the SO₄^-· played a dominant role.

With Ca(NO3)2·4H2O and Al(NO3)3·9H2O as raw materials and urea as precipitant, a precursor Ca-Al-LDHs was prepared by microwave heating and hydrothermal synthesis. A product of Ca-Al hydrotalcite (Ca-Al-LDOs) was obtained after roasting, and it was used to adsorb fluorine in wastewater. It is found that Ca-Al-LDOs are of typical layered structure similar to hydrotalcite. With pH of 2, initial concentration of F^- ion at 500 mg/g, adsorbent dosage of 2.5 g/L and reaction time of 180 min, the adsorption capacity reaches 173.9 mg/g and the removal rate of fluorine reaches 92.01%. It is found that the process of adsorption conforms to the Freundlich adsorption isotherm mode, and its kinetics conforms to the quasi-second-order kinetic model. The adsorbent Ca-Al-LDOs can be reused after desorption, with defluorination rate keeping at 68.92% after 8 cycles of regeneration.

An efficient defluorination agent (NY-Z02) was used to remove fluoride from high-salt fluoride-containing wastewater generated in the process of recycling spent batteries. The effects of pH value, reaction temperature, reaction time and dosage of defluorination agent on fluoride removal effect were investigated. On this basis, a two-stage fluoride removal process was put forward, with which a pilot test was carried out. Results show that by using a single-stage fluoride removal process, a reaction runs at 20 ℃ for 20 min with pH of 7.0 at the end and by adding defluorination agent at an amount of 1.2%, resulting in the fluoride concentration in the wastewater decreased to 12.5 mg/L. While by using a two-stage fluoride removal process, with addition of defluorination agent at an amount of 1.0%, the fluoride concentration in the wastewater can be decreased to 12.4 mg/L. In the pilot test with the dosage of defluorination agent reduced to 0.768%, the fluoride concentration in the wastewater after fluoride removal process met the requirement of enterprise (F≤20 mg/L). It is found that during the removal process with agent NY-Z02, fluoride ions in wastewater react with the agent and form precipitate of AlF₃, or together with Al(OH)₃ are removed by flocculation and precipitation. It is shown that this process has good fluoride removal effect without bringing in any impurities.

To investigate the current situation of heavy metal pollution in a stone coal mine in Hunan Province, the content of Cd, Hg, As, Pb, Cr, Cr(Ⅵ), Zn, Fe, and Mn in water and soil samples was determined by using ICP, and the risk of heavy metal pollution was evaluated by using the Nemerow pollution index and potential ecological hazard index respectively. The results show that concentrations of Cd, Cr(Ⅵ), Zn, Fe and Mn in water are 1.935 5, 0.025 3, 6.024 9, 16.222 0 and 4.214 9 mg/L on average, with pollution indices of 387.10, 5.06, 3.01, 54.07 and 42.15, presenting the pollution degree in the following descending order: Cd>Fe>Mn>Cr(Ⅵ)>Zn; while content of Pb、Zn、Cr、As、Hg and Cd in the soil is 8.51, 38.59, 18.65, 10.01, 0.18 and 3.41 mg/kg on average, with ecological risk coefficient of 2.13, 0.98, 0.85, 18.00, 28.55 and 339.80 on average, presenting pollution degree in the following descending order: Cd>Hg>As>Pb>Zn>Cr. It is shown that the comprehensive potential ecological risk indices of the whole mine is 390.31, indicating a higher ecological pollution risk. The mine area is polluted by several kinds of heavy metals, especially in the downstream areas of waste dump and sedimentation tank.

A typical metal mine with a smelter in Hunan Province was taken as an example, and 22 key factors affecting the environmental risk diffusion path of heavy metal pollution area were chosen based on data crawling and on-site case investigation, as well as systematical sorting. Nemerow integrated pollution index (NIPI) of soil was calculated using Nemerow pollution index method, and then was used to aid the identification of key factors. Results show that atmospheric deposition and soil permeability are selected as the environmental risk diffusion path for heavy metal pollution of soil based on the analytic hierarchy process, and the key factors for environmental risk diffusion include distance from pollution source, PM10 content in air, hard cover on ground surface, anti-seepage measures, soil pH value and soil organic matter (SOM) content. It is found that the NIPI of the soil is positively correlated to soil pH value, SOM, PM₁₀, but negatively correlated to the distance from pollution source, hard cover on soil surface and anti-seepage measures. The correlation coefficient fits well with the factor weight (R²=0.63).

The pollution of heavy metals in the soil of a zinc smelting site was analyzed, and the influence mechanism of goethite on cadmium migration in the soil was discussed by performing simulation experiments. The results show that the geometric mean values of As, Cd, Cu, Hg and Pb in zinc smelting site soil are 15.9 mg/kg, 1.52 mg/kg, 62.1 mg/kg, 0.108 mg/kg and 167 mg/kg respectively. The average content of Cd is 11.7 times the general value of soil in Hunan Province. It is shown that Cd in the soil has strong migration, and can be infiltrated down to the depth of 6 m or more of the soil. The results of stochastic forest model analysis show that Cd migration in the soil is mainly affected by goethite and silt. Cd in the soil can be adsorbed by goethite and then migrated. The pH value and ionic strength of leachate obviously affect the migration of Cd by goethite in the soil. When the pH of leachate is 6 and the ionic strength is 1 mmol/L, 37.6% of Cd in the soil can be migrated by goethite. Adjusting the pH value and salt ions concentration of soil can change the migration of Cd by goethite in the soil. As a result, the risk of pollution by heavy metals such as Cd in the soil of zinc smelting site can be controlled.

Acting as a raw material, mangosteen peel  was subjected to decolorization with isopropanol and activation with alkaline reagent for preparing a kind of adsorbent, which was then used to adsorb copper ions in solution. The result from an adsorption experiment shows that increasing pH value can be beneficial to the adsorption of copper ions onto mangosteen peel, with the maximum adsorption capacity up to 1.5 molCu²⁺/kg. The adsorption can reach equilibrium within 30 min. The amount of loaded copper ions has a significant effect on the characteristic temperature of thermal decomposition of adsorbents during combustion. When the concentration of copper ions is lower than 2 mmol/L, there are higher number of loaded copper ions, and the temperature at which thermal decomposition begins and violent combustion decomposition ends becomes lower. When the concentration of copper ion is higher than 2 mmol/L, the characteristic value of thermal decomposition temperature no longer changes significantly. Copper ion plays a role of catalyst in the combustion process, which can effectively promote the combustion reaction.

In order to process copper complex wastewater from electroplating industry, a kind of kaolin was  modified  by using a modifier of 3-mercaptopropyl trimethoxysilane (MPTS) to be as an  adsorbent, and its adsorption of E330-Cu was then studied. It is found that kaolin shall be properly modified at 50 ℃ for 6 hours with the modifier MPTS at an amount of 0.04 mL/g, which is then adopted as an adsorbent for E330-Cu. After 35 min- adsorption at 35 ℃, with E330-Cu at an initial concentration of 5 mg/L, adsorbent at an amount of 15 g/L, and pH value of 4.5, the final adsorption rate can reach 92.50%. It is shown that the adsorption process follows Langmuir isothermal adsorption model and quasi-second-orderkinetic model. This kind of adsorbent can be repeatedly used for at least 3 times, and the wastewater after processing can meet the national classⅠdischarge standard. This research can provide reference for the treatment of copper-containing complex wastewater from electroplating industry.

With orange residue extract and tetrasodium glutamate diacetate (GLDA) as raw materials, a green activator was prepared. Then, the effects of phosphate-solubilizing bacteria (PSB) combined with green activator on the enrichment, translocation and accumulation of cadmium from soil by ryegrass were studied. The results show that PSB can significantly promote the growth of ryegrass in cadmium-contaminated soil. However, the growth of ryegrass is inhibited by only using green activator, with the dry weight of ryegrass at the end of experiment decreased by 27.37%; while a combination of PSB and green activator can make the final dry weight of ryegrass become 1.29 times that in the blank group, indicating that the addition of PSB can alleviate the negative effect of green activator on the growth of ryegrass. A combination of both can increase the content of phytoavailable cadmium in soil, while decrease the total cadmium concentration in soil. It is shown that the enrichment coefficient of Cd in stem and root parts of ryegrass increases by 35.37% and 10.23%, respectively, and the translocation factor of cadmium by ryegrass increases by 22.58%. In addition, the total accumulation of cadmium in the stem and root parts of ryegrass is up by 87.90% and 32.69%, respectively. It is found that the total accumulation of cadmium in the stem is all greater than that in the root whether by using PSB and green activator separately, or by a combination of both, indicating that PSB combined with green activator can promote the phytoextraction efficiency of cadmium from soil by ryegrass.

Methylene blue was degraded by adopting a heterogeneous Fenton system composed of manganese residue and H₂O₂, and the effects of initial pH value, H₂O₂ concentration, dosage of manganese residue and reaction temperature on the degradation performance were studied. The reusability of manganese residue was investigated, and the removal mechanism of methylene blue in the manganese residue/H₂O₂ system was also discussed. The results show that the removal rate of methylene blue can exceed 98.1% after 120 min reaction at temperature of 25 ℃, with methylene blue concentration of 20 mg/L, H₂O₂ concentration of 10 mmol/L, manganese residue dosage of 2 g/L, and initial pH value of 2.5. After the manganese residue is recycled for 5 times, the removal rate of methylene blue can be still up to 95.5% by 300 min reaction. In the manganese residue/H₂O₂ heterogeneous Fenton system, ·OH plays a leading role in the degradation of methylene blue.

MIL-53(Fe), a metal-organic framework (MOF) material, prepared by using solvothermal synthesis was adopted to adsorb Sb(Ⅲ) in soil. MIL-53(Fe) was used as the adsorbent to adsorb the Sb(Ⅲ) in aqueous solution,  and the effects of solution temperature, pH value, adsorbent dosage, initial concentration of Sb(Ⅲ), and humic acid content on adsorption performance were explored. Then, the isotherms and kinetics of adsorption were also analyzed. After 15 d remediation with the adsorbent at an amount of 3%, the TCLP testing shows that the concentration of leachable Sb(Ⅲ) decreases by 94.2%. However, the pH value and humic acid content of the solution have little effect on the adsorption performance. For 25 mL solution with concentration of Sb(Ⅲ) at 10 μg/mL, addition of 20 mg MIL-53(Fe) can bring good adsorption effect. The initial concentration of Sb(Ⅲ) has a significant impact on the adsorption of Sb(Ⅲ) by MIL-53(Fe). At equilibrium, the maximum adsorption capacity of the adsorbent is 102.9 mg/g. The adsorption isotherm of this process fits with the Freundlich model, and its adsorption kinetics can be described using pseudo-second order model.

A kind of contaminated paddy soil was taken for pot experiment by adding FeSO₄ to investigate the impact of FeSO₄ on the formation of iron plaques on the root surface and the migration of the Cd from Cd-contaminated paddy soil. Results show that with the addition of FeSO₄ increased from 0 to 320 mg/kg, the pH value of the paddy soil tends to decline, maximally by 0.70. The TCLP-Cd content in the potting soil rises to a certain extent compared to the control group. The addition of FeSO₄ significantly reduces the Cd content in leaves, husks, and brown rice, as well as effectively increases the amount of root iron plaque, thus the absorption of Cd in the soil by rice is moderately controlled. However, the addition of external iron resource can bring impact to the pH of soil and bioavailability of Cd, so it is recommended that in practical operation, FeSO₄ should be added with some alkaline restorative materials such as lime to contaminated paddy fields for enhancing the control.

Hydrothermal carbon generated by hydrothermal carbonization of waste jujube branches was activated with zinc chloride as an activator, and a kind of modified biochar was prepared with highly porous and aromatic structure on its surface, which was then used to adsorb Zn²⁺ in aqueous solution. It is shown that for the solution with pH of 9 and initial Zn²⁺ concentration of 30 mg/L, after 80 min adsorption at a temperature of 55 ℃ by adding 700 mg/L modified biochar, the removal rate of Zn²⁺ therein exceeds 99%. The adsorption process is well-fitted to the Freundlich adsorption model, indicating that the adsorption process with the modified biochar is a multilayer molecular adsorption. The removal rate of Zn²⁺ by the modified biochar, after 5 cycles of adsorption and desorption, can still remain over 97%.

The iron-carbon (Fe-C) micro-electrolysis was adopted to treat arsenic-containing wastewater from copper smelting, and the effects of processing parameters, including pH of inlet water, air blowing rate, contacting time, vibration frequency, solid-liquid ratio (mass ratio of Fe-C micro-electrolysis material to inlet water per minute), on the arsenic removal efficiency were explored. Results show that during the treatment by Fe-C micro-electrolysis, the generated oxides such as FeAsO₄, Fe₂O₃, and Fe₃O₄ are deposited on the surface of the Fe-C micro-electrolysis material, making passivation of the Fe-C micro-electrolysis material ineffective, thus resulting in poor arsenic removal efficiency. The use of vibration can effectively solve such problem. It is shown that after 90 d continuous treatment under the conditions, including pH of inlet water at 2.0, air blowing rate at 5 L/min, contacting time of 2 min, solid-liquid ratio of 2.5∶1, vibration frequency rate at 2 min every 4 h, the arsenic removal rate can be up to 99.99% and the arsenic content in water falls down to 0.033-0.036 mg/L, presenting a good and stable removal effect. It is concluded that this arsenic removal approach by adopting Fe-C micro-electrolysis can provide a new idea for treatment of arsenic-containing wastewater from copper smelting.

Fluoride-containing industrial wastewater was treated by using a composite coagulant of polymerized aluminum chloride (PAC) and polyacrylamide (PAM), and effects of PAC dosage, PAM concentration, pH value, reaction time and stirring speed on fluoride removal efficiency were explored. The results show that by adding 4 400 mg/L PAC, with PAM concentration of 1 mg/L, solution with pH of 7.0, reaction time of 20 min and stirring speed of 300 r/min, the fluoride removal rate can reach 97.98%, leading to the residual concentration of fluoride ion at only 0.81 mg/L. However, the presence of impurity ions can reduce the fluoride removal rate by PAC.

By adjusting the pH value of electrokinetic remediation cathode and adding enhancers, the total removal rate of Cr from the contaminated soil by electrokinetic remediation technology was increased. Then, the change of energy consumption and law of Cr migration and distribution during the electrokinetic remediation project were explored. The results show that EDTA, citric acid and hydrochloric acid can significantly enhance the total Cr removal rate during the electrokinetic remediation process. The total removal rates of Cr were 24.47% and 23.24% respectively after 7 days of electrokinetic remediation without adjusting the pH value of the cathode, by adding EDTA and citric acid into the soil. The pH value of the cathode isn't adjusted, which results in an obvious polarization effect. In contrast, the total removal rates of Cr were 44.20% (4.9 times as much as the blank) and 36.80%, respectively, after 7 days of electrokinetic remediation with the pH value of the cathode controlled, by adding hydrochloric acid and citric acid to the soil, respectively. Controlling the pH value of the cathode can effectively prevent the precipitation of Cr in the cathode region, thus enhancing the removal rate of Cr, but won't significantly increase the energy consumption of the electrokinetic remediation process. This method can greatly increase the total removal rate of Cr in contaminated soil by electrokinetic remediation, which is of significance in guiding the remediation of heavy metal contaminated soil.

Red mud was pre-treated with process of reduction roasting followed by magnetic separation, and the obtained non-magnetic material was calcined and then dissolved in hydrochloric acid. After that, it was filtered after addition of saturated sodium meta-aluminate polymerizing agent, and then matured to prepare polymeric aluminum chloride (PAC) base liquid, which was used in a purification test. With PAC-base liquid and manganese-containing wastewater in a volume ratio of 1∶120, stirring speed of 140 r/min, pH of 8, reaction temperature of 30 ℃, and addition of polyacrylamide (PAM) at an amount of 20 mg/L, the manganese mass concentration in the wastewater reduced from 325.3 mg/L to 1.5 mg/L after 5 hours of settlement, showing manganese removal rate up to 99.5%. It is shown that the manganese mass concentration in the purified liquid can meet class Ⅰ limit in the national  discharge standard.

Based on comparison of cadmium immobilization with 4 types of minerals originated from 14 places in Hunan Province, four kinds of natural and efficient remediation materials (including limestone from Yujiaao of Ningxiang County, low-grade manganese ore from Nanmuchong of Xiangtan County, bentonite from Mazongling of Taoyuan County, and sepiolite from Xingang of Shimen County) were selected. The kinetic rate of cadmium immobilization by these four natural minerals is in the following descending order: bentonite > limestone > sepiolite > manganese ore. The cadmium adsorption by four kinds of minerals increases as the initial cadmium mass concentration increases. With cadmium mass concentration no higher than 10.0 mg/L, the cadmium adsorption by these four minerals is in the following descending order: limestone > bentonite > manganese ore > sepiolite; with cadmium mass concentration exceeding 10.0 mg/L, the cadmium adsorption by these four minerals is in the following descending order: bentonite > limestone > manganese ore >sepiolite. The adsorption behavior follows Langmuir adsorption model, and the maximum adsorption capacities of bentonite, limestone, manganese ore and sepiolite are 29.38 mg/g, 14.51 mg/g, 9.67 mg/g and 5.27 mg/grespectively. With pH of solution within the range of 6 to 9, the removal efficiency of cadmium by four minerals is in the following descending order: limestone > bentonite > manganese ore > sepiolite. It is concluded that the cadmium immobilization with natural minerals is related to  chemical composition of minerals,  initial cadmium mass concentration, and pH value.