Single, binary and multi-component adsorption of some anions and heavy metals on environmentally friendly Carpobrotus edulis plant

A low-cost adsorbent and environmentally friendly adsorbent from Carpobrotus edulis plant was used for the removal of NO(3)(-), H(2)PO(4)(-), Pb(2+) and Cd(2+) ions from single, binary and multi-component systems. The efficiency of the adsorbent was studied using batch adsorption technique under different experimental conditions by varying parameters such as pH, initial concentration and contact time. In single component systems, the dried C. edulis has the highest affinity for Pb(2+), followed by NO(3)(-), Cd(2+) and H(2)PO(4)(-), with adsorption capacities of 175mg/g, 125mg/g, 28mg/g and 26mg/g, respectively. These results showed that the adsorption of NO(3)(-) and H(2)PO(4)(-) ions from single and binary component systems can be successfully described by Langmuir and Freundlich isotherms. Freundlich adsorption model, showed the best fit to the single and binary experimental adsorption data. These results also indicated that the adsorption yield of Pb(2+) ion was reduced by the presence of Cd(2+) ion in binary metal mixture. The competitive adsorption of NO(3)(-), H(2)PO(4)(-), Pb(2+) and Cd(2+) ions on dried C. edulis plant shows that NO(3)(-) and H(2)PO(4)(-) anions are able to adsorb on different free binding sites and Pb(2+) and Cd(2+) cations are able to adsorb on the same active sites of C. edulis particles. The dried C. edulis was found to be efficient in removing nitrate, phosphate, cadmium and lead from aqueous solution as compared to other adsorbents already used for the removal of these ions.     

Renewable molybdate complexes encapsulated in anion exchange resin for selective and durable removal of phosphate

The existence of many anions in wastewater reduces the removal efficiency of phosphate by adsorbents under realistic conditions. Facing this challenge, the study reports on an insistent and stable composite adsorbent of molybdate complexes Fe-(MoO_x) embedded in a macroporous anion exchange resin (D-201). [Fe(MoO_x)]-D-201 shows 93.7% adsorption capacity (28.3 mg/g) for phosphate even when the molar concentration of coexisting ions is 5 times higher than phosphate. The capacity of adsorbent is maintained more than 84.2% after five regeneration cycles to remove phosphate in the wastewater containing coexisting ions. The ability of highly selective removal of phosphate is maintained during the regeneration cycles explained by the change of the binding of molybdate clusters with phosphate, which is due to the different structures of molybdate clusters depending on various pH. In general, this work puts forward a new idea for the development of phosphorus removal adsorbents for the treatment of wastewater containing coexisting ions.     

镁铝二元水滑石的焙烧产物对染料废水酸性红88的吸附

研究了镁铝水滑石的焙烧产物(LDO)对阴离子染料废水酸性红88(AR88)的吸附特征。分别考察了染料的初始浓度、吸附剂投加量、初始pH值、反应温度和竞争离子等因素的影响,并用XRD、红外光谱对水滑石以及吸附前后的LDO进行了表征。实验结果表明：LDO对高浓度的AR88具有良好的去除效果,在15 ℃、pH=10～11下,1.0 g·L^-1的LDO对浓度为2 000 mg·L^-1的AR88的去除率可高达99.95%,吸附容量为1 999.0 mg·g^-1。经4次回收重复利用的LDO对AR88的去除率仍为90%以上。     

Phosphate adsorption on synthetic goethite and akaganeite

Low crystalline iron hydroxides such as goethite (alpha-FeOOH) and akaganeite (beta-FeOOH) were synthesized, and the selective adsorption of phosphate ions from phosphate-enriched seawater was examined. The results of the distribution coefficients (K(d)) of oxoanions in mixed anion solutions at pH 8 follow the selectivity order Cl-, NO3-, SO4(2-) < CO3(2-), HPO4(2-) for goethite, and Cl-, CO3(2-) < NO3- < SO4(2) < HPO4(2-) for akaganeite. In seawater, both adsorbents show high selectivity for phosphate ions despite the presence of large amounts of major cations and anions in seawater. The adsorption isotherms fitted better with the Freundlich equation and the maximum uptake of phosphate from phosphate-enriched seawater was 10 mg P/g at an equilibrium phosphate concentration of 0.3 mg P/L on both adsorbents. The phosphate adsorption/desorption cycles show that akaganeite is an excellent adsorbent even after 10 cycles and its chemical stability is good.     

Removal of phosphate using copper-loaded polymeric ligand exchanger prepared by radiation grafting of polypropylene/polyethylene (PP/PE) nonwoven fabric

A novel polymeric ligand exchanger (PLE) was prepared for the removal of phosphate ions from water. 2,2′-dipyridylamine (DPA), a bidentate ligand forming compound with high coordination capacity with a variety of metal ions was bound to glycidyl methacrylate (GMA) grafted polypropylene/polyethylene (PP/PE) nonwoven fabric synthesized by radiation-induced grafting technique. DPA attachment on epoxy ring of GMA units was tested in different solvents, i.e. methanol, ethanol, dioxane and dimethylsulfoxide (DMSO). The highest amount of modification was achieved in dioxane. In order to prepare the corresponding PLE for the removal of phosphate, DPA-immobilized fabric was loaded with Cu(II) ions. Phosphate adsorption experiments were performed in batch mode at different pH (5–9) and phosphate concentrations. The fabric was found to be effective for the removal of phosphate ions. At every stage of preparation and use, the nonwoven fabric was characterized by thermal (i.e. DSC and TGA) and spectroscopic (FTIR) methods. Competitive adsorption experiments were also carried out using two solutions with different concentration levels at pH 7 to see the effect of competing ions. Phosphate adsorption was found to be effective and selective from solutions having trace amounts of competitive anions. It is expected that the novel PLE synthesized can be used for the removal of phosphate ions in low concentrations over a large range of pH.     

纯相钙铝层状双氢氧化物对磷的吸附特性

采用乙醇辅助液相共沉淀法制备了纯相Ca-Al-LDH层状双金属氢氧化物,考察了Ca-Al-LDH的投加量、吸附时间、pH值、无机电解质(Na₂CO₃ ,KCl ,Na₂SO₄,KNO₃)和温度等因素对磷吸附的影响,结果表明,纯相Ca-Al-LDH对磷酸根离子具有很好的吸附性能,最大饱和吸附量可达160.78 mg/g,当pH值为5.1、温度为45 ℃、吸附时间为600 min、LDH投加量为0.6 g/L、磷初始浓度为80 mg/L时,磷的去除率高达95.88%;无机阴离子会抑制磷在吸附剂上的吸附,当Cl^-浓度从2.5 g/L升高到25 g/L时,Ca-Al-LDH对磷酸盐的最大饱和吸附量从69.96 mg/g降至53.18 mg/g,降低了23.99%;当SO₄^2-浓度从2.5 g/L升高到25 g/L时,Ca-Al-LDH对磷酸盐的最大饱和吸附量降低了24.79%,其它无机阴离子对磷在吸附剂上的吸附也有一定的影响。 Ca-Al-LDH对水中磷的吸附符合二级动力学方程和Langmuir等温模型。 采用扫描电子显微镜、傅里叶变换红外光谱仪和X射线衍射仪等技术手段对制备的纯相Ca-Al-LDH及其吸附磷酸根后的产物进行表征,揭示了Ca-Al-LDH对磷酸根的吸附可能是静电吸引、化学吸附和阴离子插层等过程协同作用的吸附机理。     

A review on adsorption mediated phosphate removal and recovery by biomatrices

Low cost biosorbents have gained considerable importance in the past decade for their removal efficiency of contaminants from wastewaters. Both removal and recycle of the phosphate anion through benign methods are relevant to sustain a steady balance. An attempt has been made to give a comprehensive insight into several physico-chemical factors leading to the adsorption process by various natural biosorbents. Few important facts regarding phosphate biosorption have emerged out as key points viz., pH < pHpzc, high uptake capacity; correlation with Langmuir isotherm model and pseudo second order kinetics; decrease of uptake capacity with longer contact time; enhancement of adsorption process in presence of counter ions, etc. Also, it was noted that the adsorbate: adsorbent ratio is crucial for the removal efficiency of the phosphate ions. A few biosorbents exhibit removal efficiency to a large extent (>95%) although even higher adsorption capacity can be obtained by the modification of the adsorbents. Commercial biomatrices like biochars have shown wide applications for removal of phosphates. Magnetic biochars have shown special performance owing to the presence of iron and a porous nature of their structure. Desorption studies revealed that almost complete recovery of the phosphate ion is possible through simple ion exchange mechanism.     

Equilibrium and kinetic studies of adsorption of phosphate onto ZnCl2 activated coir pith carbon

Phosphate removal from aqueous solution was investigated using ZnCl₂-activated carbon developed from coir pith, an agricultural solid waste. Studies were conducted to delineate the effect of contact time, adsorbent dose, phosphate concentration, pH, and temperature. The adsorption equilibrium data followed both Langmuir and Freundlich isotherms. Langmuir adsorption capacity was found to be 5.1 mg/g. Adsorption followed second-order kinetics. The removal was maximum in the pH range 3–10. pH effect and desorption studies showed that adsorption occurred by both ion exchange and chemisorption mechanisms. Adsorption was found to be spontaneous and endothermic. Effect of foreign ions on adsorption shows that perchlorate, sulfate, and selenite decreased the percent removal of phosphate.     

Synthesis, characterization, thermodynamic and kinetic investigations on uranium (VI) adsorption using organic-inorganic composites: Zirconyl-molybdopyrophosphate-tributyl phosphate

Zirconyl-molybdopyrophosphate-tributyl phosphate (ZMPP-TBP) was a novel organic-inorganic composite adsorbent prepared by co-precipitation method and used in the adsorption of uranium from aqueous solution in batch adsorption experiments. The as-obtained product was characterized using SEM, energy dispersive X-ray spectroscopy (EDX), XRD and BET-N₂ adsorption measurements. The study had been conducted to investigate the effects of solution pH, temperature, contact time, initial concentration and coexisting ions. A maximum removal of 99.31% was observed for an initial concentration 5 mg/L, at pH 6.0 and an adsorbent dose of 1.0 g/L. The isothermal data were fitted with both Langmuir and Freundlich equations, but the data fitted the former better than the latter. According to the evaluation using the Langmuir equation, the maximum adsorption capacity of uranium (VI) was 196.08 mg/g at 293 K and pH 6.0. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the kinetic data, and the pseudo-second-order kinetic model was better. The thermodynamic parameter ΔG was calculated, the negative ΔG values of uranium (VI) at different temperature showed that the adsorption process was spontaneous. The good reusability of ZMPP-TBP also indicated that the ZMPP-TBP was a very promising adsorbent for uranium adsorption from aqueous solution.     

Copper (II) adsorption from aqueous solution by herbaceous peat

In this research, the herbaceous peat collected from Gavurgolu peatlands, one of the biggest Turkish peatlands, was utilized as an adsorbent for the removal of copper (II) ions from aqueous solution. Adsorption experiments were conducted under various conditions, i.e., initial concentration, temperature, and pH. While the amount of Cu (II) adsorbed on the peat increased with increasing concentration of Cu (II) ions, it was not markedly affected by temperature and pH. Percentage removal was higher at lower concentration. For example, the maximum percentage removal of Cu (II) ions for initial concentration of 3 x 10(-4) M was 97.04% at 21 degrees C and pH 5.5. The adsorption capacity (Q(0)) of the peat was 4.84 mgg(-1) from Langmuir adsorption isotherm for the concentration range of 3 x 10(-4)-6 x 10(-4) M at 21 degrees C and pH 5.5. The equilibrium time of adsorption of Cu (II) ions was 150 min and independent of concentration and temperature. The amount of Cu (II) adsorbed at equilibrium time did not considerably change with temperature and pH. It was also determined that adsorption isotherm followed both Freundlich and Langmuir. Uptake mechanism of Cu (II) ions by the peat occurs via cation exchange (especially by means of Ca(2+) and Mg(2+)) as well as copper/peat complexation. Adsorption kinetic was consistent with the pseudo-second-order model.     

Removal of Cd(II) and Pb(II) from aqueous solution by modified attapulgite clay

Three low-cost adsorbents (purified raw attapulgite (A-ATP), high-temperature-calcined attapulgite (T-ATP), and hydrothermal loading of MgO (MgO-ATP)) were prepared as adsorbents for the removal of Cd(II) and Pb(II). By evaluating the effect of the initial solution pH, contact time, initial solution concentration, temperature and coexistence of metal ions on Cd(II) and Pb(II) adsorption, the experimental results showed that MgO-ATP was successfully prepared by hydrothermal reaction and calcination as well as appearing to be a promising excellent adsorbent. At an initial pH of 5.0, A-ATP, T-ATP and MgO-ATP reached maximum adsorption amounts of 43.5, 53.9 and 127.6 mg/g for Pb(II) and 10.9, 11.2, and 25.3 mg/g for Cd(II) at 298 K, respectively. The Cd(II) adsorption on A-ATP was fitted by the Freundlich model, while the adsorption of Pb(II) and Cd(II) on T-ATP and MgO-ATP as well as Pb(II) adsorption on A-ATP agreed with the Langmuir model. All kinetic experimental data favored pseudo second-order model. The calculated thermodynamic parameters suggested that Pb(II) adsorption onto MgO-ATP was spontaneous and exothermic. When considering foreign metal ions, the three adsorbents all presented preferential adsorption for Pb (II). Chemical adsorption had a high contribution to the removal of Cd(II) and Pb(II) by modified attapulgite. In summary, the adsorption was greatly enhanced by the hydrothermal loading of MgO. It aimed to provide insights into the MgO-ATP, which could be able to efficiently remove Cd(II) and Pb(II) and serve as an economic and promising adsorbent for heavy metal-contaminated environmental remediation.     

Hydroxyapatite-coated carboxymethyl chitosan scaffolds for promoting osteoblast and stem cell differentiation

This study investigated the potential of MIEX resin as the adsorbent for the removal of phosphate from aqueous solutions. In our batch experiments, we studied the effect of some parameters on the removal of phosphate. It was observed that uptake of phosphate was mainly affected by initial phosphate concentration, adsorbent dosage, initial pH of solution, and coexistent anions. The adsorption equilibrium data at 288 K fitted well to Freundlich and Koble-Corrigan isotherm models. The kinetics studies displayed that the adsorption process followed the pseudo-second-order model. The diffusion studies showed that the intra-particle diffusion was not the only rate-controlling step and, the diffusion process of phosphate from solution to MIEX resin was controlled by film diffusion. The thermodynamics parameters were evaluated. The results showed that the adsorption process was spontaneous thermodynamically, endothermic, and entropy driven. These results have established a good potentiality for MIEX resin to be used as an adsorbent for the removal of phosphate from aqueous solutions. This work will deepen our understanding of the adsorptive characteristics of phosphate by MIEX resin and provide a better way to remove phosphate from wastewater.     

Adsorption of fluoride, phosphate, and arsenate ions on a new type of ion exchange fiber

A new type of ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions has been developed. A batch adsorption technique for investigating adsorption kinetic and equilibrium parameters and determining pH adsorption edges is applied. It is shown that the adsorption properties of the ion exchange fiber for fluoride, phosphate, and arsenate ions depend on the pH value and anion concentration. The adsorption of arsenate on the sorbent reaches a maximum of 97.9% in the pH value range of 3.5 to 7.0. The adsorption percentage of phosphate is more than 99% in the pH range of 3.0 to 5.5. The adsorption of fluoride on the ion exchange fiber is found to be 90.4% at pH 3.0. The Freundlich model can describe the adsorption equilibrium data of fluoride, arsenate, and phosphate anions. The sorption of the three anions on the ion exchange fiber is a rapid process, and the adsorption kinetic data can be simulated very well by the pseudo-second-order rate equation. The column performance is carried out to assess the applicability of the ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions from synthetic wastewaters with satisfactory removal efficiency. The desorption experiment shows that fluoride ion sorbed by the fiber column can be quantitatively desorbed with 5 mL of 0.50 mol/L NaOH at elution rate of 1 mL/min, and 30 mL of NaOH is necessary for the quantitative recovery of phosphate and arsenate ions.     

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.     

Preparation of quaternized dimethylaminoethylmethacrylate grafted nonwoven fabric for the removal of phosphate

Dimethylaminoethylmethacrylate (DMAEMA) grafted polyethylene/polypropylene (PE/PP) nonwoven fabric was prepared by radiation-induced graft polymerization. Grafting conditions were optimized and about 150% DMAEMA grafted samples were used for further experiments. DMAEMA graft chains were later quaternized with dimethyl sulphate for the removal of phosphate ions. Adsorption experiments were conducted with quaternized DMAEMA grafted fabric for phosphate removal at low (0.5–25 ppm) and high phosphate concentrations (50–1000 ppm). Adsorbed phosphate amounts at pH 7 were found to be 63 mg phosphate/g polymer and 512 mg phosphate/g polymer for low (25 ppm) and high phosphate concentrations (1000 ppm) respectively showing the efficiency of the adsorbent material in removing phosphate. The pH effect on phosphate adsorption showed that the quaternized DMAEMA grafted nonwoven fabric can adsorb phosphate over a wide pH range (5.00–9.00) indicating that adsorbent material can effectively remove different forms of phosphate ions, namely H₂PO₄^?, HPO₄^2? and PO₄^3? in aqueous solution at this pH range where the species exist. Competitive adsorption experiments were also carried out with two concentration levels at pH 7 to investigate the effect of competing ions. Phosphate adsorption on quaternized DMAEMA grafted nonwoven fabric was found to be higher than the other competing ions at two concentration levels. At high concentration level, the adsorption order was phosphate>nitrite>bromide>sulphate>nitrate whereas at low concentration level, the order was phosphate?sulphate>bromide>nitrite>nitrate.     

Increasing the arsenate adsorption capacity of neutralized red mud (Bauxsol)

The possibility of increasing the arsenate adsorption capacity of seawater-neutralized red mud (Bauxsol) through acid treatment, combined acid and heat treatment, and the addition of ferric sulfate (Fe(2)(SO(4))(3).7H(2)O) or aluminum sulfate (Al(2)(SO(4))(3). 18H(2)O) is investigated. The results show that acid treatment alone, as well as in combination with heat treatment increases the removal efficiency, with the combination providing the best removal. Adding ferric sulfate or aluminum sulfate, however, suppress the removal. The results also show that activated Bauxsol (AB) produced using combined acid and heat treatment can remove roughly 100% arsenate (at pH 4.5) with or without competing anions (i.e., phosphate, bicarbonate, and sulfate) when the initial arsenate concentration is < or = 2 mgl(-1). Furthermore, it is found that the adsorption process using AB is not accompanied by the release of unwanted contaminants, and TCLP results indicate that the spent AB is not hazardous. It is believed that the AB produced here has good potential as an alternative adsorbent to conventional methods for removing arsenate from water.     

Treatment of methyl orange by calcined layered double hydroxides in aqueous solution: adsorption property and kinetic studies

Adsorption of a weak acid dye, methyl orange (MO) by calcined layered double hydroxides (LDO) with Zn/Al molar ratio of 3:1 was investigated. In the light of so called "memory effect," LDO was found to recover their original layered structure in the presence of appropriate anions, after adsorption part of MO(-) and CO(2-)(3) (come from air) intercalated into the interlayer of LDH which had been supported by XRD and ICP. The results of adsorption experiments indicate that the maximum capacity of MO at equilibrium (Q(e)) and percentage of adsorption (eta%) with a fixed adsorbent dose of 0.5 g L(-1) were found to be 181.9 mg g(-1) and 90.95%, respectively, when MO concentration, temperature, pH and equilibrium time were 100 mg L(-1), 298 K, 6.0 and 120 min, respectively. The isotherms showed that the adsorption of MO by Zn/Al-LDO was both consistent with Langmuir and Freundlich equations. The adsorption process was spontaneous and endothermic in nature and followed pseudo-second-order kinetic model. The calculated value of E(a) was found to be 77.1 kJ mol(-1), which suggests that the process of adsorption of methyl orange is controlled by the rate of reaction rather than diffusion. The possible mechanism for MO adsorption has also been presumed. In addition, the competitive anions on adsorption and the regeneration of Zn/Al-LDO have also been investigated.     

Effective adsorption of Hg(II) ions by new ethylene imine polymer/β-cyclodextrin crosslinked functionalized magnetic composite

A new effective magnetic composite material was prepared successfully for adsorption Hg(II) ions by introducing β-cyclodextrin/ethylene imine polymer to the mesoporous silica. The morphology and structure of EIP-β-CD magnetic adsorbents were characterized by FT-IR, XR, DTG, XPS and SEM technologies. The effect of many factors were discussed detailedly such as adsorption time, initial concentration, pH, different composition of adsorbent and adsorption temperature. It was found that EIP-β-CD showed excellent adsorption capacity, high selectivity, good reutilization and fast adsorption rate. The maximum adsorption capacity was 248.72 mg/g and the best removal rate was 99.49 % under the optimized experimental conditions. The kinetic and thermodynamic study showed typical characteristic of chemical adsorption, exothermic and spontaneous. The best mass proportion of β-cyclodextrin, ethylene imine polymer and glutaraldehyde was 1.0:0.4:0.2, and proper β-cyclodextrin can develop the adsorption capacity for Hg(II) ions in this adsorbent. The possible adsorption mechanism was investigated in detail. After the fifth cycle experiment, this new adsorbent still showed excellent adsorption capacity which indicated that it has great potential for Hg(II) ions cleanup in water solution.     

Removal of cadmium(II) and zinc(II) metal ions from binary aqueous solution by rice husk ash

The present study reports the competitive adsorptive removal of cadmium (Cd(II)) and zinc (Zn(II)) ions from binary systems using rice husk ash (RHA), a waste obtained from the rice husk-fired furnaces, as an adsorbent. The initial pH (pH₀) affects significantly the capacity of RHA for adsorbing the metallic ions in the aqueous solution. The pH₀ ≈ 6.0 is found to be the optimum for the removal of Cd(II) and Zn(II) ions by RHA. The single ion equilibrium adsorption from the binary solution is better represented by the non-competitive Redlich–Peterson (R–P) and the Freundlich models than by Langmuir model in the initial metal concentration range of 10–100 mg/l. The adsorption of Zn(II) ion is more than that of Cd(II) ion, and this trend is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with increasing concentrations of the other metal ion and the combined effect of Cd(II) and Zn(II) ions on RHA is generally found to be antagonistic. Non-modified Langmuir, modified Langmuir, extended-Langmuir, extended-Freundlich, Sheindorf–Rebuhn–Sheintuch (SRS), non-modified R–P and modified R–P adsorption models were tested to find the most appropriate competitive adsorption isotherm for the binary adsorption of Cd(II) and Zn(II) ions onto RHA by minimizing the Marquardt's percent standard deviation (MPSD) error function. The extended-Freundlich model satisfactorily represents the adsorption equilibrium data of Cd(II) and Zn(II) ions onto RHA.     

荞麦皮生物吸附去除水中Cr(Ⅵ)的吸附特性和机理

农业废弃物荞麦皮作为生物吸附剂去除水中Cr(Ⅵ),研究了荞麦皮对Cr(Ⅵ)的去除动力学以及溶液pH、吸附剂用量和Cr(Ⅵ)初始浓度对去除效率的影响;通过FT-IR,XPS,SEM-EDX对荞麦皮表面组成和结构进行表征,探索荞麦皮去除Cr(Ⅵ)的机理.结果显示:荞麦皮对Cr(Ⅵ)有很高的去除效率.常温下5.0 g·L-1的荞麦皮在pH=2.0下对100 mg·L-1 Cr(Ⅵ)溶液的去除率可达99.87%.荞麦皮对Cr(Ⅵ)的去除率随溶液pH降低而升高,在pH=2.0时达到最大;随吸附剂用量增加而增大;随Cr(Ⅵ)初始浓度增加而减小.单位质量荞麦皮对Cr(Ⅵ)的去除量随吸附剂用量增加而减小;随Cr(Ⅵ)初始浓度增加而增加,最后趋于稳定.在20℃,pH=2.0,吸附用量为5.0 g·L-1时,荞麦皮对Cr(Ⅵ)的最大去除容量约为36.4 mg·g-1.荞麦皮吸附去除Cr(Ⅵ)的过程符合准二级吸附动力学.FT-IR,XPS和SEM-EDX分析结果表明:荞麦皮是一个多孔材料,表面存在羧基、氨基、羟基等活性基团;荞麦皮对Cr(Ⅵ)的去除是一个吸附-还原耦合的过程,包括Cr(Ⅵ)在荞麦皮表面上的静电吸附,以及此后的固相还原和对还原态的Cr(Ⅲ)再吸附;Cr(Ⅲ)的吸附主要是通过与荞麦皮表面的羧基、氨基的配位,以及与其中的阳离子发生离子交换作用实现的.