Selective adsorption of chromium(VI) from zinc(II) and other metal ions using persimmon waste gel

An adsorption gel was prepared from persimmon waste, a cellulosic material, rich in polyphenolic compounds, which exhibits a high affinity for chromium(VI). It was prepared by cross-linking persimmon waste with concentrated sulphuric acid. Adsorption tests for different metal ions such as Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at pH values ranging from (pH 1 to 5) found Cr(VI) to be selectively adsorbed on the cross-linked gel over the other metal ions studied. The adsorption isotherm of Cr(VI) followed the Langmuir type of adsorption and exhibited a maximum loading capacity of 7.18 mol kg^− 1 at pH 1. Selective removal of Cr(VI) from Zn(II) was successfully demonstrated by using a column packed with the persimmon waste gel.     

Alkane-insoluble trialkylammonium double salts involving the dodecamolybdophosphate anion. I. Model studies using trioctylamine in dodecanol-modified nonane

Third-phase formation in the extraction of Mo(VI) from dilute H₂SO₄ containing phosphate by 0.05 M tri-n-octylamine (TOA) in nonane modified with n-dodecanol can be attributed to molybdate-phosphate condensation reactions leading to the appearance of dodecamolybdophosphate (DMP) anion, PMo₁₂O₄₀³⁻, as the dissolved amine salt (TOAH)₃ [DMP]. The condensation reaction was briefly examined showing that after small amounts of Mo(VI) are initially extracted, at least partly in the form of a molybdophosphate intermediate, the DMP anion forms in a slow, quantitative reaction over a period of several weeks. What little ability the solvent has to dissolve the condensation product (TOAH)₃ [DMP] appears to involve a solubilizing mixed-salt interaction with other amine salts in the system, raising the solvent tolerance for (TOAH)₃ [DMP] well above the value for the modified nonane alone (< 10⁻⁷M). Even so, DMP-containing third phases form at (TOAH)₃ [DMP] concentrations less than 1.3 × 10⁻⁴M, the exact tolerance varying within a limited range as a function of (1) the proportion of the amine sulfate which is converted to the chloride form via anion exchange with aqueous chloride and (2) the dodecanol : TOA mole ratio at constant (0.05 M) TOA molarity. Two types of third phases form, both having mixed-salt compositions. When the system contains sufficient chloride, the solid double-salt compound (TOAH)₃ [DMP] · 3(TOAH)Cl precipitates at the interface. When the system is deprived of chloride, a dense, liquid third phase forms consisting of the amine DMP, sulfate, and bisulfate salts plus nonane and possibly water. Technological implications are discussed in terms of hydrometallurgical applications of amine extraction. The double salt (TOAH)₃ [DMP] · 3(TOAH)Cl may be important in understanding compound formation between two alkylammonium salts containing different anions.     

Effect the tungsten(VI) and molybdenum(VI) ions on the electrical conductivity of ammonium hydroxide solutions

The effect of the W(VI) and Mo(VI) ions on the electrical conductivity of ammonium hydroxide solutions (7 mol/L) is studied in the tungsten or molybdenum concentration range 0.1–0.5 mol/L and the temperature range 20–60°C. The electrical conductivities of the solutions are shown to depend linearly on the solution temperature and the metal concentration, and the coefficients of linear regression equations are calculated. The temperature coefficients of the electrical conductivities of the solutions are determined.     

Simultaneous Removal of Cd and Cr(VI) Using Fe-Loaded Zeolite

Current research focuses on the simultaneous removal of Cd and Cr(VI) in water by a newly developed material having both abilities of sorption and electrochemical reduction. The material was derived from the zeolite modified by Fe(II) chloride followed by sodium borohydride reduction. The Fe-loaded zeolite simultaneously removed Cd and Cr(VI) to below the detection limit at a fairly rapid rate within 1?h for Cd and within 20?h for Cr(VI), under the pH ranging from slightly acid to around neutral. At high concentration of coexisting Cr(VI), the removal efficiency of Fe-loaded zeolite for Cd slightly decreased due to surface fouling by Cr(III) hydroxide precipitations. On the contrary, the coexisting Cd was found to increase the removal rate of Cr(VI) by Fe-loaded zeolite. From the test results, the Fe-loaded zeolite was found to be a possible alternative in simultaneous removal of Cd and Cr(VI) in the aqueous phase.     

A solvent extraction study of silver(I), palladium(II) and mercury(II) with 2-tert-dodecylthiopyridine

2-tert-Dodecylthiopyridine was synthesized from 2-chloropyridine and tert-dodecanethiol in order to examine its extraction properties for various metals. It was found to have good selectivity for the extraction of palladium(II) and mercury(II) over platinum(II) and -(IV) and base metals from chloride media; silver(I) was found to be almost completely extracted from nitric acid (0.01–5 mol/dm³ HNO₃). Palladium(II) and mercury(II) were completely extracted from hydrochloric acid over the range 0.01–2 and 0.01–0.5 mol/dm³ HCl, respectively. The rate of extraction of palladium(II) from hydrochloric acid was much faster than when using dialkylsulfide and triisobutylphosphine sulfide extractants. An aqueous mixture of thiourea and hydrochloric acid was found to be effective as stripping solution for palladium(II). The extent of stripping was dependent on the concentrations of either thiourea or hydrochloric acid.     

The measurement of the diffusion coefficient of U(VI) in aqueous uranyl sulfate solutions

The diffusion coefficients of U(VI) in aqueous uranyl solutions were determined between 293.5 and 311.0 K by comparing the limiting current densities between the copper electrodeposition and the electrolytic reduction of uranyl sulfate under the same hydrodynamic condition. The diffusion coefficients thus determined were almost constant despite the change in agitation speed of electrolyte solutions, which suggests the appropriateness of the method employed in this study. On the other hand, the diffusion coefficients of U(VI) showed a slightly decreasing trend with increase in uranyl sulfate concentration, but when total uranium concentration was kept constant the diffusion coefficient appeared to be almost constant. The activation energies of diffusion coefficients of U(VI) were found to be 21 to 22 kJ mol⁻¹ for the solution studied. KOJI SATO formerly Graduate Student, Department of Metallurgy, Kyoto University, Kyoto, Japan     

The kinetics of the solvent extraction of cobalt (II) and lead (II) with versatic acid

In the solvent extraction of cobalt (II) and lead (II) from aqueous ammonium nitrate solutions with Versatic 10 in hexane, initial extraction rates were measured at 303 K using a Lewis-type stirred transfer cell. In the extraction of cobalt(II), the initial extraction rate expression was found to be described by N = κ₁C_AW/[H⁺] in the high concentration region of Versatic 10 and by N = κ_IIC_AWC_BO²/[H⁺]² in the low concentration region of Versatic 10. An interfacial reaction mechanism was proposed in order to give a reasonable interpretation of the observed rate expressions. In the extraction of lead(II), the initial extraction rate at low pH was found to be described also by the second rate expression shown above. At high pH, the rate is independent of hydrogen ion concentration. From this result, it was presumed that only the non-hydrated aquo-cation of lead(II) takes part in complex formation at the interface.     

An increase in purity of ammonium perrhenate solutions with respect to molybdenum(IV) with the sorption recovery of rhenium(VII) from Mo-containing solutions

The possibility of the additional purification of ammonia rhenium desorbates with respect to molybdenum in the course of the sorption recovery of rhenium from Mo-containing solutions with the help of Purolite A170 and Purolite A172 weak base anion-exchange resins is considered. The pH-dependence of sorption of Re(VII) and Mo(VI) on these anion-exchange resins is investigated in static conditions with the 1 M (NH₄)₂SO₄ background in the solution. It is shown that the range of pH, in which anion-exchange resins retain the ability to sorb Re(VII), is also spread to a weakly basic region. A substantial decrease in the adsorption of Re(VII) starts already with an increase in pH above 7.5. The capacity of anion-exchange resins with respect to Mo(VI) starts to decrease noticeably with an increase in pH of solutions above 5.0, and molybdenum almost ceases to sorb by both anion-exchange resins upon reaching pH ~ 7.0. In order to decrease the Mo(VI) content in rhenium desorbates with the sorption recovery of Re(VII) from Mo-containing solutions on weak base anion-exchange resins, the following flowsheet is suggested. Initially, the main amount of sorbed Mo(VI) is desorbed by contacting the saturated anion-exchange resin with the ammonium sulfate solution upon mixture stirring and holding constant pH of the solution in limits of 7.0–7.5 due to the addition of dosed amounts of ammonia solution. Then anion-exchange resin is separated from the ammonium sulfate solution containing Mo(VI), washed with water, and Re(VII) is desorbed by ammonium solution in dynamic conditions. The verification of the proposed method for the resins saturated by sorption from the model solution of the composition, g/L, 98 H₂SO₄, 4 Mo(VI), and 0.5 Re(VII) showed the occurrence of desorption of no less than 90% sorbed molybdenum during the treatment of anion-exchange resins with ammonium sulfate solution. Herewith, concentration ratio Re(VII) : Mo(VI) in ammoniacal rhenium desorbates when using A170 anion-exchange resin increases 11-fold and when using A172 anion-exchange resin, it increases 20-fold compared with that attained without the additional washing of Mo(VI). Losses of Re(VII) with the Mo-containing desorbate (reversible) do not exceed 5.2% of the amount of sorbed Re(VII).     

Liquid extraction of rhenium(VII) and molybdenum(VI) with trialkylphosphine oxide from acidic solutions

The liquid extraction of rhenium(VII) and molybdenum(VI) ions from sulfuric, hydrochloric, and nitric acid media is studied in the temperature range from 20 to 40°C using trialkylphosphine oxide in kerosene as an extracting agent. The maximum separation of these metals is attained when they are extracted from solutions of 1.0–2.0 M H₂SO₄ (the duration of intense phase mixing was 3–5 min). The enthalpy of the studied process is estimated to be ΔH = ?32.32 kJ/mol for molybdenum and ?51.52 kJ/mol for rhenium. The chemical aspects of the extraction process studied are discussed.     

Lanthanum(Ⅲ) sorption studies on poly[dibenzo-18-crown-6] and its separation from uranium(Ⅵ) and thorium(Ⅳ) in L-valine medium

The sorption study of La(Ⅲ) was carried out on poly[dibenzo-18-crown-6] and L-valine medium. The quantitative adsorption of La(Ⅲ) was found at 1x10-2 to 1x10-5 mol/L L-valine. The various eluting agents were found efficient eluents for La(Ⅲ). The capacity of crown polymer for La(Ⅲ) was found to be 0.43 ±0.01 mmol/g. The tolerance limit of various cations and anions for La(Ⅲ) was determined.La(Ⅲ) was quantitatively separated from other metal ions in binary as well as multicomponont mixtures. The study was extended to sequen-tial separation of La(Ⅲ), U(Ⅵ) and Th(Ⅳ). The good separation yields were obtained and had good reproducibility (±2%). The method in-corporated the determination of La(Ⅲ) in real sample. The method was simple, rapid and selective.     

New agents for in vivo chelation of uranium(VI): efficacy and toxicity in mice of multidentate catecholate and hydroxypyridinonate ligands

Soluble uranyl ion [UO2(2+), U(VI)] is a kidney poison. Uranyl ion accumulates in bone, and the high specific activity uranium isotopes induce bone cancer. Although sought since the 1940's, no multidentate ligand was identified, until now, that efficiently and stably binds U(VI) at physiological pH, promotes its excretion, and reduces deposits in kidneys and bone. Ten multidentate ligands patterned after natural siderophores and composed of sulfocatechol [CAM(S)], carboxy-catechol [CAM(C)], or hydroxypyridinone [Me-3,2-HOPO] metal-binding units have been tested for in vivo chelation of U(VI). Ligands were injected intraperitoneally (i.p.) into mice 3 min after intravenous (i.v.) injection of 233U or (232+235)U as UO2Cl2 [ligand-to-metal molar ratio 75 to 92]. Regardless of backbone structure, denticity, or binding unit, all 10 ligands significantly reduced kidney U(VI) compared with controls or with mice given CaNa3-DTPA, and four CAM(S) or CAM(C) ligands also significantly reduced skeleton U(VI). Several ligands removed U(VI) from kidneys, when injected at 1 or 24 h. Injected at molar ratios > or = 300, 5-LIO(Me-3,2-HOPO) and TREN-(Me-3,2-HOPO) reduced kidney U(VI) to about 10% of control. Given orally to fasted mice at molar ratios > or = 300, those ligands significantly reduced kidney U(VI). In mice injected i.v. with 0.42 micromol kg(-1) of 235U and given 100 micromol kg(-1) of one of those Me-3,2-HOPO ligands i.p. daily for 10 d starting at 1 h after the U(VI)) loss of kidney U(VI) was greatly accelerated, and the kidneys of treated mice showed no microscopic evidence of renal injury. Crystals of uranyl chelates with linear tetradentate ligands containing bidentate Me-3,2-HOPO groups demonstrate a 1:1 structure. Considering low toxicity, effectiveness, and reasonable cost, the structurally simple linear tetradentate ligands based on the 5-LI backbone (diaminopentane) offer the most promising approach to a clinically acceptable therapeutic agent for U(VI). Work is in progress to identify the most suitable CAM or HOPO binding unit(s).     

Solvent extraction of uranium(VI) from industrial and analytical grade phosphoric acid using organic extractants in kerosene with variable content of aromatic hydrocarbons

The distribution ratio of U(VI) between phosphoric acid, industrial and analytical grade, and kerosene solutions of D2EHPA-TOPO extractants with variable amount of aromatic hydrocarbons has been studied. Under these conditions it was observed that the content of aromatic hydrocarbons in the diluent as well as other ions present in industrial phosphoric acid play a significant role in the extraction of uranium(VI).     

A novel extractant bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide for cerium(IV) extraction and separation from sulfate medium

By introducing the amine group into phosphorus extractant, a novel aminophosphine compound bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide (DEHAPO, abbreviated as A) was synthesized for the extraction of cerium (IV) (Ce(IV)) from sulfate medium (H₂SO₄). The influence factors including extractant concentration, H₂SO₄ concentration and temperature on the Ce(IV) extraction were investigated and discussed. It is found that the extraction ability of Ce(IV), thorium (IV) (Th(IV)) and rare earths (REs(III)) (La, Gd, Yb) decreases in sulphate medium in the following order: Ce(IV) > Th(IV) > REs(III). The extraction process is an exothermic reaction and the thermodynamic parameters were calculated. The extracted complex of Ce(HSO₄)₂SO₄·A in loaded organic solution was identified by the slope methods and further proved by FT-IR spectral analysis. Stripping studies indicate that Ce(IV) can be effectively stripped from the organic phase. The results of separation factors (β) and saturation loading capacity demonstrate that DEHAPO could be used to selectively extract Ce(IV) from sulphate medium with high separation efficiency and good extraction ability.     

Laboratory reduction rate and current efficiency studies of batch type electrolytic reduction of U(VI) in a sulfate system

The electrolytic reduction of U(VI) was investigated to improve the batch type electrolytic reduction of uranyl sulfate. For this purpose, theoretical considerations were made on the time variation of reduction rate and of current efficiency. A monitoring device consisting of two titanium electrodes and one platinum electrode was developed to determine the reduction ratio and to detect the end point of the reduction of U(VI). The monitoring device worked well for these purposes. The reduction rate in a batch type electrolytic reduction of U(VI) at constant current was larger than theoretically expected. This phenomenon was attributed to the increase in the mass transfer rate of U(VI) species toward the cathode due to the disturbance of the concentration boundary layer by hydrogen gas evolved from the cathode surface. The deterioration of titanium cathode experienced in an operating plant was investigated, and was found to be caused by platinum plating onto the titanium cathode surface during the operation. The deteriorated cathode could be restored by immersing it in a hot aqua regia or a mixture of hydrofluoric acid and phosphoric acid for a few minutes.     

Solvent extraction of Ti(IV), Fe(III) and Fe(II) from acidic sulfate medium with di-o-tolyl phosphoric acid-benzene — hexan-1-ol system: A separation and mechanism study

The extraction of Ti(IV), Fe(III) and Fe(II) with di-o-tolyl phosphoric acid (HDTP, HA)-benzene-20% hexan-1-ol system was studied as function of contact time, concentrations of extractant in the organic phase and of H₂SO₄ in the aqueous phase, and temperature. The order of extractability under identical conditions is: Ti(IV) > Fe(III) ? Fe(II). The relative separations of these metal ions are also dependent on the above four factors. The maximum values of the separation factors, $\text{β}{}_1\text{=}\text{E}{}_{\mathrm{<mtext>Ti(IV)</mtext>}}{}^0\text{E}{}_{\mathrm{<mtext>Fe(IlI)</mtext>}}{}^0\text{= 175}$ at 0.10 M HDTP and 3.50 M H₂SO₄ concentrations, and $\text{β}{}_2\text{=}\text{E}{}_{\mathrm{<mtext>Ti(IV)</mtext>}}\text{E}{}_{\mathrm{<mtext>Fe(II)</mtext>}}{}^0\text{= 7800}$ at 0.10 M HDTP and 0.50 M H₂SO₄ concentrations, indicate that the separation of Ti(IV) from iron seems to be promising if iron is present in the divalent state. The mechanisms of extraction are discussed.     

生物聚合硫酸铁去除U(VI)的絮凝试验

采用生物聚合硫酸铁絮凝剂对低浓度含铀废水进行絮凝试验研究,考察U(VI)溶液pH、絮凝剂投加量以及U(VI)初始浓度对絮凝效果的影响。结果表明,反应最佳pH范围在5~7,反应平衡时间为5 min,其絮凝过程符合Lagergren准二级反应动力学模型。含铀废水经生物聚合硫酸铁絮凝处理过后,残余铀浓度低于《铀加工与燃料制造设施辐射防护规定》（EJ 1056-2005）中的排放限值（0.05 mg/L）。     

纳米零价镍去除溶液中U(VI)的研究

采用液相还原法制备纳米零价镍,并用来去除溶液中的U(VI)。通过SEM、EDS技术表征反应前后材料的形貌,从微观角度分析纳米零价镍去除溶液中U(VI)的机理,并进行了热力学分析。结果表明,纳米零价镍对溶液中U(VI)有良好的去除效果,在室温下,pH=4.0、接触时间60min、固液比0.3g/L和初始浓度50mg/L时,U(VI)的去除率和去除量分别达到了98.44%和182.372mg/g。新制备的纳米零价镍呈明显的球状,颗粒较为分散且粒径较均匀,反应后,材料表面形貌发生变化,呈不规则碎片堆积、粒径变大,且材料中出现了铀元素。热力学研究结果表明,该反应是自发吸热反应,同时也是不可逆的熵增反应。     

Enzymatic reduction of chromium(VI) by human hepatic microsomes

The reduction of chromium(VI) by human hepatic microsomes was investigated. The reduction rates were proportional to the amount of microsomes added and reduction was mediated by an NADPH-dependent enzymatic system which exhibited a Km for chromate of 1.04 +/- 0.18 microM and a Vmax of 5.03 +/- 0.49 nmol/min/mg protein. Relative to incubation under 0% O2, 21% O2 inhibited microsomal Cr(VI) reduction in three individuals by 53, 36 and 37%. Cr(VI) reduction was not inhibited by metyrapone, carbon monoxide, aminopyrine, piperonyl butoxide or chloroform, suggesting that cytochrome P450s did not play a major role. Thallium trichloride (0.13 and 0.26 mM), a known flavoprotein inhibitor, caused a complete inhibition of both Cr(VI) reduction and NADPH:cytochrome P450 (c) reductase activity. A partial inhibition of Cr(VI) reduction was seen in the presence of n-octylamine, which may suggest a possible role for flavin-containing monooxygenase (FMO). Overall, human microsomal Cr(VI) reduction is very different from the P450-mediated microsomal reduction observed in rodents. Specifically, the human system is much less oxygen-sensitive, has a much greater affinity for chromate and is apparently mediated by flavoproteins.     

A study about the mechanism of hepatocyte injury induced by endotoxin--interaction of Kupffer cells and polymorphonuclear neutrophils (PMNs)

Focusing our attention on the TNF (tumor necrosis factor) produced by Kupffer cells (KCs). The role of KCs and polymorphonuclear neutrophils (PMNs) in endotoxin (LPS)-induced hepatocellular injury was investigated. This study used the culture fluid supernatant of KCs which had been stimulated with LPS as the "LPS stimulation supernatant", and evaluated hepatocellular injury as ornithine carbamyl transferase percent leakage. There was no difference between groups I (HCs: hepatocytes) and II (HCs + PMNs), but there were differences between groups I and III (HCs + LPS stimulation supernatant, groups II and IV (HCs + LPS stimulation supernatant + PMNs), and III and IV. There was no significant difference between III and V (III + anti-TNF antibody), but a difference was found between IV and VI (IV + anti-TNF antibody). These findings suggest that PMNs activated by KCs-generated TNF as well as KCs-derived humoral factors other than TNF play a role in the development of LPS-induced hepatocellular injury.     

Extraction of gold(III) in hydrochloric acid solution using monoamide compounds

The extraction and separation properties of Au(III) using two monoamide compounds, N,N-di-n-octylacetamide (DOAA) and N,N-di-n-octyllauramide (DOLA), which have different side chain lengths attached to the carbonyl carbon (CH₃ for DOAA and n-C₁₁H₂₃ for DOLA), were investigated. The solvent extraction of some precious and base metals (Au(III), Pd(II), Pt(IV), Rh(III), Fe(III), Cu(II), Ni(II) and Zn(II)) in HCl solutions was carried out using DOAA and DOLA diluted with n-dodecane and 2-ethylhexanol. A good selectivity for Au(III) extraction with 0.5 M extractant is obtained at lower HCl concentrations (< 3.0 M) in both systems. The extractability of Au(III) with DOAA is greater than that with DOLA. In the 0.5 M DOAA–3.0 M HCl system, a third phase is formed when the Au(III) concentration in the initial aqueous phase is over 39 g/L. In contrast, third phase formation is not found in the 0.5 M DOLA–3.0 M HCl system, and its loading capacity of Au(III) is about 79 g/L. The Au(III) extracted in the organic phase is effectively back-extracted by 1.0 M thiourea in 1.0 M HCl solution in both systems, while some thiourea is precipitated using the organic phase containing 20 g/L of Au(III). The back extraction of Au(III) using water is poor in the DOAA system, but possible in the DOLA system.