柠檬酸工业废水强化镉污染土壤的电化学法修复

通过批量解吸附实验和电化学修复实验,研究利用柠檬酸工业废水作为电化学修复的增效剂从高缓冲容量的天然土壤中去除镉的可行性。批量实验结果表明,当加入柠檬酸工业废水时,85%以上的镉能在土壤pH≤5.0的条件下从土壤中溶解到溶液中;在pH5.0～8.0范围内镉的解吸附率比用去离子水增加20%～45%。电化学修复实验结果表明,与相同pH值的HNO₃相比,该废水作为电极溶液可使镉在土壤中发生明显迁移;在距离阳极0～4 cm及8～10 cm处土壤镉含量由282 mg·kg^-1降低至167～200 mg·kg^-1,而在距阳极4～8 cm处土壤镉含量升高至约400 mg·kg^-1。经过514 h的电化学修复,约84.7%的镉可以从土壤中去除,其中约94.6%从土壤中去除的镉富集在阴极溶液中。可见柠檬酸工业废水是一种非常有前景的重金属污染土壤电化学修复增效剂。     

Removal of cadmium and lead from soil using aescin as a biosurfactant

Remediation of a soil contaminated with cadmium or lead was performed by a soil washing process using aescin as a biosurfactant. The removal of cadmium and lead from the soil was evaluated as a function of aescin concentration and pH in a batch process. A 30-mM aescin solution was most effective in the removal of cadmium and lead at pH 6.8. Cadmium and lead migrated from the soil to the aescin-containing aqueous phase, depending on the pH value. We found that 41% of cadmium (pH 7.8) and 25% of lead (pH 2.8) in the soil matrix migrated into a 30-mM aescin solution. Also, the complexation of aescin with cadmium and lead ions was confirmed by Fourier transform infrared spectroscopy and electrical conductivity measurements. As a result, the maximal complexation capacity of aescin with metal ions was approximately aescin/cadmium=2∶1 and aescin/lead=3∶1 on a molar basis. It was suggested that aescin may sequester cadmium and lead ions by the carboxylic and saccharide moieties. Then, the complex of aescin with cadmium or lead may migrate to the aqueous phase as the result of dispersion.     

Study on the performance of Cd2+ sorption using dimethylethylenediamine-modified zinc-based MOF (ZIF-8-mmen): optimization of the process by RSM technique

ABSTRACT

Cadmium as a highly toxic metal is released into the environment through paper production, metal processing, phosphate fertilizers, insecticides, and treatment of wastewater. Cadmium also inhibits the body activities and is very toxic for kidney and other organisms. In the current study, zinc-based metal–organic framework, zeolitic imidazolate framework (ZIF)-8, was synthesized and modified by dimethylethylenediamine (ZIF-8-mmen) for the removal of cadmium. To optimize the experiments, response surface methodology was applied with three variables including pH, adsorbent dosage, and contact time using central composite design. The optimum conditions for pH, dosage, and time were 2, 0.1 g, and 89 min, respectively, with removal efficiency of 85.38%. The Langmuir isotherm (q _m = 1000 mg/g) indicates the monolayer adsorption. The kinetic studies reveal that the Lagergren model was predominant and cadmium was not chemisorbed. Thermodynamic parameters show spontaneous, endothermic, and physisorption processes.     

Cadmium concentration in vegetable crops grown in a sandy soil as affected by Cd levels in fertilizer and soil pH

Field trials were conducted over a three-year period with chinese cabbage (Brassica pekinensis Rupr.) and carrots (Daucus carota L.) grown in a sandy soil with pH adjusted to 5.5 and 6.5. The NPK fertilizers containing 1, 30, 90, and 400 mg Cd kg^–1 P were applied at the rate of 0.07, 2.1, 6.3 and 28 g Cd ha^–1 yr^–1. The amounts of Cd added through phosphate rock also ranged between 0.1 and 28 g ha^–1 yr^–1. The increased Cd application rates through NPK fertilizers increased the Cd concentration in both vegetables but the differences among treatments were not found to be significant. The Cd uptake by both crops was significantly (p<0.01) higher at pH 5.5 than at pH 6.5. Chinese cabbage exhibited lower Cd concentration than carrots. Carrot leaves contained higher Cd than its roots. Cadmium removals by chinese cabbage and carrot were about 0.7 and 1.3 g ha^–1 yr^–1, respectively. At pH 5.5, Cd concentrations in the two crops, based on a three-year average, were 23 and 46% higher than at pH 6.5. Cadmium uptake by chinese cabbage from different sources of phosphate rock was affected to a very limited extent. Cadmium concentration generally increased over the years. Cadmium extracted by ammonium nitrate after harvest of the crops was closely related with soil pH and Cd concentration in the plants.     

Uptake and allocation of plant nutrients and Cd in maize,sunflower and tobacco growing on contaminated soil and the effect of soil conditioners under field conditions

Contaminated land may in many cases still be used for agriculture, provided that crops are chosen appropriately, as the accumulation of contaminants varies greatly among cultivars and also plant parts. We aimed to determine whether maize (Zea mays), sunflower (Helianthus annuus) and tobacco (Nicotiana tabaccum) grown on a heavy-metal contaminated soil containing copper (540 mg Cu kg⁻¹), zinc (680 mg Zn kg⁻¹) and cadmium (1.4 mg Cd kg⁻¹) could be used to gradually remediate the soil, while producing valuable biomass. The soil was treated with either a normal fertiliser regime (control), elemental sulphur (S), or the biodegradable chelant NTA (nitrilotriacetic acid), to test how soil acidification or chelating organic compounds would affect the uptake and allocation of selected elements (Ca, Cd, Cu, Fe, K, Mg, Mn, P, S and Zn). The highest concentrations of Cd, Cu and Zn occurred in the leaves and/or roots, while seeds and grains contained much lower concentrations of these elements. All these concentrations, however, were still in the ranges considered normal for the respective plant parts grown on uncontaminated soil. While sunflower and maize could be safely used as food and feed, tobacco would better be used for bioenergy than for cigarette production because of its relatively high foliar Cd concentration. The two treatments (S and NTA) had only slight effects on the uptake and allocation of plant nutrients and Cd. Thus, there was little benefit of these treatments for phytoextraction purposes at this site.     

Cadmium and zinc adsorption onto activated carbon: Influence of temperature,pH and metal/carbon ratio

The adsorption characteristics of cadmium and zinc onto a granular activated carbon were studied. Cadmium and zinc removals increased on raising pH and temperature, and decreased on raising the molar metal/carbon ratio. The adsorption processes were modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall bidentate species. A dependence of the SCF constant on pH, the molar metal/carbon ratio and temperature was observed, and a correlation for log K_ads was determined. The SCF model successfully predicted cadmium and zinc removals.     

Untersuchungen über Cadmiumgehalte in Leinsaat (Linum usitatissimum L.)

Investigations on Cadmium Contents of Linseed (Linum usitatissimum L.) Cadmium contents have been analyzed in linseed (Linum usitatissimum L.) material derived from a country-wide model-trial and with 16 genotypes grown at 5 locations in the Federal Republic of Germany. Among 118 samples out of the model-trial, which are devided in nearly equal parts of the cultivars Antares and Atalante, a range of cadmium contents between 0.1 and 1.7 mg/kg (100 and 1700 ppb) were found. Here, a general difference between these two cultivars was obvious, in that half of the samples of Atalante were below the threshold value of 300 ppb; in Antares only about a quarter of the samples were below this level. This finding was confirmed by the results of the trial with 16 different genotypes, which indicates that genotypic differences in uptake and accumulation of cadmium really do exist in linseed. The results of the trials also demonstrate, that linseed low in Cd-content can be produced only at suitable locations.     

Modeling Cadmium Adsorption by Activated Carbon Using the Langmuir and Freundlich Isotherm Expressions

Abstract

Cadmium adsorption isotherms were conducted using two commercially available powdered activated carbons (PACs). Isotherms were conducted at several pH values and metal and carbon concentrations. Both PACs removed significant amounts of cadmium, and removal was a strong function of solution pH: increasing the solution pH increased cadmium adsorption. Adsorption data at a specific pH were successfully modeled using both the Langmuir and Freundlich isotherms. Adsorption and surface precipitation were hypothesized to be the operative removal mechanisms. Cadmium removal is strongly related to the carbon's pH_zpc, acid-base characteristics, and surface charge-pH relationship. Surface area, an important adsorption parameter for organic adsorbates, does not appear to influence metal removal strongly.     

Experimental study and mathematical model on remediation of Cd spiked kaolinite by electrokinetics

An experimental study on electrokinetic removal of cadmium from kaolinitic clays is presented in this work, which is aimed to investigate the effect of surface reactions on the electrokinetic process. Enhanced electrokinetic tests were performed in which the pH of the compartments was controlled. Cadmium spiked kaolin was adopted in the experimental runs. On the basis of the experimental results, a numerical model was formulated to simulate the cadmium (Cd) transport under an electric field by combining a one-dimensional diffusion-advection model with a geochemical model: the combined model describes the contaminant transport driven by chemical and electrical gradients, as well as the effect of the surface reactions. The geochemical model utilized parameters derived from the literature, and it was validated by experimental data obtained by sorption and titration experiments. Electrokinetic tests were utilized to validate the results of the proposed model. A good prediction of the behaviour of the soil/cadmium ions system under electrical field was obtained: the differences between experimental and model predicted profiles for the species considered were less than 5% in all the examined conditions.     

Biogenic hydroxyapatite synthesis by Bacillus subtilis: An efficient passivator for the reduction of cadmium contamination in agricultural soil

Cadmium (Cd) can cause various diseases and threaten human health through its accumulation in crops. In this study, Bacillus subtilis was used to prepare biogenic hydroxyapatite (B-HAP), and chemical hydroxyapatite (C-HAP) without microorganisms was produced as the control. The abilities of B-HAP and C-HAP to adsorb Cd in aqueous solutions and passivate the migration of Cd in actual soil were analyzed. In the adsorption experiments, the Cd concentration in the solutions decreased by 94.8% and 95.8% when 0.20 mmol of B-HAP and C-HAP were added. In the incubation experiment, the soil pH increased from 7.08 to 7.30 and from 7.08 to 7.43 when 0.021% of B-HAP and C-HAP were added. B-HAP had little disturbance to the soil pH value. The results showed that Cd in the mobilizable state, at 0.021% B-HAP and C-HAP, respectively, decreased by 38.6% and 36.8% in the actual soil samples. The structure and morphology of B-HAP were characterized using various techniques, which indicated that the adsorption mode of B-HAP would change with time from ion exchange to specific adsorption. Therefore, B-HAP can be used as an effective passivator for Cd removal from agricultural soil. The concentrations of Olsen-P decreased by 35% when 0.021% B-HAP was added after 104 days. This study provides insights into the development of novel passivators that benefit soil health and green development and has reference significance for the eco-friendly regulation of low-concentration-Cd–contaminated agricultural soil.     

The effect of apatite and elemental sulphur mixtures on growth and P content ofCentrocema pubescens

Two glasshouse pot experiments and one incubation experiment were undertaken to measure the effectiveness of Sri Lanka (Eppawala) apatite rock phosphate as a fertilizer for the perennial legumeCentrocema pubescens. The apatite was applied alone, or as a mixture with elemental sulphur and soil containingThiobacelli bacteria either as powder or pellets that were either uncoated or coated with rubber (to reduce the rate of release of P thereby increasing P release for a longer-term).Application of apatite to the soil significantly increased DM yields of shoots and P content (yield × P concentration) in shoots. Application of sulphur andThiobacelli bacteria with the apatite caused further increases in yield and P contents of shoots. Pelletizing the apatite and sulphur together with a soil inoculum ofThiobacillus did not increase dry matter yields of shoots or P content of shoots compared to a mixture of apatite and sulphur in the powder form. Incubating the mixture in powder or pellet form in the laboratory increased water-soluble P extracted and decreased the pH of these mixtures. Pellets of the mixture when coated with rubber released P more slowly during incubation, but growth ofCentrocema pubescens treated with coated pellets was comparable with that for uncoated pellets.     

Extractive Separation and Direct Colorimetric Determination of Cadmium with Thiothenoyltrifluoroacetone

Abstract

Thiothenoyltrifluoroacetone (STTA) was used for the quantitative extraction of cadmium at tracer level. Cadmium was extracted completely at pH 6.5-7.5 with 0.001 M STTA in carbon tetrachloride as the yellow colored complex which could be measured colorimetrically at 450 nm. The system adhered to Beer's law in the concentration range of 0.9 to 19 μg/ml. The complex was stable for at least 96 hr. Ten milliliters 0.001 M STTA in carbon tetrachloride was adequate for quantitative extraction of cadmium. The optimum period of equilibration was 10 min. It was possible to effect extractive separation and colorimetric determination of cadmium in the presence of 1 : 200 of alkali, alkaline earths, thallium, germanium, and organic complexing acids. Other ions were tolerated in the ratio ≥ 1 : 20. The method was rendered selective by using sequestering agents, such as citric acid, tartaric acid, or alkali cyanide, or by resorting to selective extraction process with either tributylphosphate or acetylacetone.     

Nutrient recycling potential of Tephrosia candida in cropping systems of southeastern Nigeria

Improving fallow quality in cassava–fallow rotations in southeastern Nigeria through the use of leguminous cover crops has been shown to sustain the productivity of such systems. We studied the effects of age (1 or 2 years) of Tephrosia candida fallow on biomass and nutrient accumulation, on weed biomass and yield response of cassava/maize intercrop and on changes in soil chemical properties in a 3 yr field trial. Results were compared with those obtained in natural fallow. Total biomass and litter were three times higher in plots fallowed for 2 yr with Tephrosia candida than in those under natural fallow for the same period. Weed biomass was 205% lower in T. candida plots fallowed for 2 yr than in the natural fallow and was 174% smaller in T. candida plots fallow for 1 yr than in the natural fallow. Nutrient (nitrogen, phosphorus, calcium, magnesium and potassium) yields in leaves of T. candida fallow for 2 yr were on average 200–300% higher than in leaves of other fallows. The same trend was observed for cassava and maize yields. Soil chemical changes at soil depth 0 to 5 cm showed significant increases in N and C concentrations after 2 yr fallowing and a year of cropping, particularly in the planted fallow plots. Conversely, soil pH, available P and the exchangeable cations, especially Ca were lower, while Al was higher than the initial values, mainly in plots fallowed under T. candida, indicating a tendency of this fallow species to further exacerbate the soil acidification problem of the acid Ultisol at the study site in southeastern Nigeria.     

The effect of fertilizer additions on the solubility and plant-availability of Cd, Ni and Zn in soil

We conducted a pot experiment to investigate the effect of fertilizer additions on the solubility of Cd, Ni and Zn in soil solution and their uptake by plants. Radish (Raphanus sativus cv. Crystal Ball), oat (Avena sativa cv. Thule) and water spinach (Ipomoea aquatica cv. Kangkon) were grown in a naturally metal-rich soil. From day 7 after planting, fertilizers were added daily to each pot. Additions of fertilizer nutrients affected the pH of soil and soil solution, soluble and tissue concentrations of Ca, Mg, K, Cd, Ni and Zn differently in three plant species. The trend of soil and solution pH was in the order: water spinach < radish < oats, that resulted highest soluble and plant tissue concentrations of Cd and Zn in the water spinach followed by radish and then oats. However, Ni concentration in the soil solution increased in all pots and was not affected by pH changes. Soil solution pH increased by more than 1unit in the pots with radish and oats, indicating that mechanisms other than acidification, such as ion exchange and root exudation, may be responsible for the increased heavy metal uptake in these two plant species. Paired t-test showed significantly higher uptake of Cd and Zn in the radish plants resulting in lower concentrations of these elements in the solution. The contribution of mass flow to the supply of major cations and heavy metals varied among elements and plant species. Cadmium, Zn and K were taken up rapidly by all plant species in response to the amount supplied by mass flow. In contrast, the supply of Ni was in excess of its uptake by radish and water spinach. The uptake of all elements was positively correlated (p<0.0001) with mass flow and the transpiration rate in individual plant species. The study suggests that fertilizer cations increased the uptake of metals by improving growth conditions, but the magnitude of increase depended on plant species. This revised version was published online in November 2006 with corrections to the Cover Date.     

Redox chemistry of H2S oxidation by the British Gas Stretford Process Part. II: Electrochemical behaviour of aqueous hydrosulphide (HS−) solutions

Electrochemical techniques were used to study the oxidation of HS^– ions at pH 9.3. Voltammetry of gold electrodes in HS^– -containing solutions showed that multilayers of sulphur and soluble oxidation products were formed. As a known HS^– oxidation product, thiosulphate solutions were also studied voltammetrically, but found to be electro-inactive at mildly oxidising potentials. The voltammetric behaviour of polysulphide ions, S _n ^2– (n = 2 to 5), was similar to that of HS^– solutions on oxidation, though they could be reduced to HS^– ions at low potentials. Ring-disc electrode experiments, extending the HS^– concentration range that had been studied previously, confirmed that polysulphide ions were produced on reduction of anodically deposited elemental sulphur. This was demonstrated in both cyclic Volammetry and potential step experiments. By comparison of the charges passed producing polysulphides from sulphur and reducing them to HS^– ions, an average polysulphide chain length of 1.8 was calculated, indicating a mixture of species was produced. Ion chromatography confirmed that polysulphide solutions do contain a number of species, consistent with thermodynamic predictions.     

Equilibrium and kinetic modelling of the adsorption of Cd ions onto chestnut shell

A study on the removal of Cd²⁺ ions from aqueous solutions by acid formaldehyde pretreated chestnut (Castanea sativa) shell was conducted in batch conditions. The influence of different parameters: adsorption time, temperature (15, 25 and 35 °C) and initial concentration of Cd²⁺ ions (15.3, 50.5 and 87.3 mg L^− 1), on cadmium uptake was analysed. Cadmium free and cadmium loaded chestnut shell were characterized by FTIR spectroscopy, which evidenced the functional groups involved in cadmium uptake. Cadmium adsorption equilibrium could be described by the Freundlich adsorption model at all the temperatures essayed, which predicted shell heterogeneity. The Cd²⁺ adsorption process by chestnut shell followed the pseudo second order kinetic model. Cadmium sorption capacity increased with decreasing temperature at an initial concentration of 15.3 mg L^− 1 and with increasing initial cadmium concentration at a temperature of 25 °C. The second order kinetic constant, which increased with increasing temperature, was used to calculate the energy of adsorption as equal to 19.2 kJ mol^− 1.     

Cadmium removal byJuniperus monosperma: The role of calcium oxalate monohydrate structure in bark

This study suggests that calcium oxalate monohydrate overJuniperus monosperma bark is an ion-exchangeable site for cadmium adsorption on the basis of its cadmium adsorption behavior and surface characterization. Cadmium adsorption behavior showed that juniper bark had a higher cadmium adsorption capacity (84.6 Μmol Cd g^-1 at pH 5) than juniper wood (32.0 Μmol Cd g⁻¹ at pH 5), and that the base-treatment improved the cadmium adsorption capacity of only juniper wood. This difference between juniper bark and wood might have originated from different cadmium binding sites. In calcium displacement, the cadmium uptake onto juniper bark was identical to the amount of calcium ions displaced, which indicated that calcium played an important role in cadmium adsorption onto juniper bark. X-ray diffraction (XRD) results gave evidence that only juniper bark contained the structure of calcium oxalate monohydrate. Furthermore, cadmium adsorption decreased the intensity of the characteristic XRD peaks for calcium oxalate monohydrate. In diffuse reflectance infrared Fourier transform (DRIFT) spectra, existence of oxalate on juniper bark was proven again and interpretation on IR band of carbonyl groups matched significantly the cadmium adsorption behavior.     

Investigation of the Column Performance of Cadmium(II) Biosorption by Cladophora crispata Flocs in a Packed Bed

ABSTRACT

In this study the biosorption of cadmium(II) ions to dried floes of Cladophora crispata, a kind of green algae, was investigated in a packed bed column. The cadmium(II) removal performance of the column was investigated as a function of the cadmium(II)-bearing solution flow rate and the inlet cadmium(II) concentration. Re- moval and total removal percentages of cadmium(II) related to flow volume were determined by evaluating the breakthrough curves obtained at three different flow rates for two different constant inlet concentrations. At the lowest flow rate the effect of inlet cadmium(II) concentration on the column capacity was also investigated. Data confirmed that early saturation and lower cadmium(II) removals were observed at higher flow rates and at higher cadmium(H) concentrations. Column experiments also showed that maximum specific cadmium(II) uptake values of C. crispata floes were as higher as those of other biomass sorbents.     

Cadmium(II) biosorption from aqueous solutions using Hydrilla verticillata

The kinetics and equilibrium of cadmium biosorption from aqueous solutions were investigated using fresh tissues of Hydrilla verticillata. The biosorptive characteristics of cadmium ions were studied with respect to well‐established effective parameters, including pH, temperature and contact time. The biosorptive capacity of H. verticillata for cadmium increased with increasing pH. In addition, the resulting isotherms were well‐described by Langmuir and extended Langmuir models (R² = 0.9794–0.9957 and 0.9880, respectively). The comparison between calculated and experimental q_e values showed that the extended Langmuir model had a better simulation for the cadmium biosorption by H. verticillata than the Langmuir isotherm model. The equilibrium biosorption data at a constant temperature were well‐interpreted by the Langmuir model. The maximum biosorptive capacity increased from 33.54 to 37.46 mg/g when the solution temperature was increased from 278 to 298 K. Other various thermodynamic parameters were also estimated. Biosorptive equilibrium was established within approximately 20 min. Moreover, the pseudo‐second‐order equation was more appropriate in predicting biosorptive capacity than the pseudo‐first‐order equation. In practical viewpoints, the abundant and inexpensive plant biomass H. verticillata can be used as an effective and environmentally friendly biosorbent for the detoxification of cadmium from aqueous solutions. © 2012 Canadian Society for Chemical Engineering     

Improvement of leguminous vegetables production in calcareous soil by addition of some acidifying materials

Two field experiments were carried out in two sites of Noubaria Agricultural Research Station Farm. The investigated acidifying materials were sulphur, superphosphate and Phosphorine. The materials were mixed with cowpea seeds just before sowing in a rate 1 kg for seeds required to 1 fed (4200 m²) in the first experiment. Additions were 100, 30 and 1 kg S, P₂O₅ and Phosphorine/fed, respectively to soils before common bean planting in the second experiment where the two varieties Giza 3 and Giza 6 were put under investigation. The residual effect of the soil additions was investigated using bean as a test crop.The obtained results showed that acidification materials were effective in such soil for seed yields of cowpea and common bean - while the residual effect on bean was unconsiderable. The variety Giza 6 of common bean was significantly superior to Giza 3. The harvesting index was higher by using sulphur or superphosphate than Phosphorine in the case of cowpea while in common bean superphosphate and Phosphorine were more active in increasing this index than sulphur. Acidification process resulted in some increases in harvest index of bean regardless the used material. As for 100 seed weight, it was raised in significant level by using sulphur or superphosphate than Phosphorine or control in the case of cowpea while all treatments were statistically equal in the case of common bean and bean.