英文翻译.docx

1、英文翻译Removal of chromium (III) and cadmium (II) from aqueous solutionsAbstractChromium and cadmium are toxic heavy metals present in wastewaters from a variety of industries. A strong cation exchange resin, Amberlite IR 120, was used for the removal of chromium and cadmium. The resin was prepared in

2、two different cationic forms, as Na + and H +. The optimum conditions were concentration, pH, stirring time and resin amount. The concentration range was between 2-50 rag/L, pH range between 2-10, stirring time between 5-60 min, and the amount of resin was from 50-1000 rag. Exchange capacities, mois

3、ture content and optimum conditions of this resin were determined in a batch system. The stirring speed was 2000 rpm during all of the batch experiments. The initial and final chromium and cadmium amounts were determined by atomic absorption spectrophotometry. The optimum conditions were found to be

4、 a concentration of 20 mg/L, pH of 5.5, stirring time of 20 min and 100 mg of resin. The results obtained show that the Amberlite IR 120 strong cation-exchange resin performed well for the removal and recovery of chromium and cadmium.Keywords: Chromium(III); Cadmium(II); Ion-exchange resins; Toxicit

5、y; Conservative technologies1. Introduction Both metals are common and important water pollutants. They are often discharged simultaneously from a variety of industrial sources including electroplating rinse waters. Due to their toxicity even at low concentrations, the maximum levels allowed of meta

6、ls are regulated by legislation in each country. The release of large quantities of heavy metals into the natural environment has resulted in a number of environmental problems. Cadmium, which is widely used and extremely toxic at relatively low dosages, is one of the principal heavy metals responsi

7、ble for causing these problems. The main anthropogenic pathway through which cadmium(II) and chromium(III) enter the environment is via wastes from industrial processes. As heavy metals cannot be destroyed in the natural environment,technologies that can remove and recovery heavy metals from wastewa

8、ter are needed. Classical techniques of heavy metal removal from solutions include the following processes: precipitation, electrolytic methods, ion exchange, evaporation and adsorption. Chemical precipitation is currently the most widely used treatment technique for removal of heavy metals. Neverth

9、eless, particularly frustrating aspects of this method are significant sludge production, the ever-increasing cost for landfill disposal of the resulting toxic sludge, and most importantly, the long-term environmental consequences .Therefore, alternative treatment processes for the removal and possi

10、bly the recovery of toxic metals have to be applied. Sorption, used here as a general term including several mechanisms such as ion exchange, surface complexation, etc., is considered as a common treatment method in many water and wastewater treatment schemes, regulating also the transport of chemic

11、al species in aquatic systems. Activated carbon, biomass and ion exchange are commonly used for removal of heavy metals. Chromium is used in a variety of industrial applications, including etectroplating and as a corrosion inhibitor in cooling towers. Chromium salts are used to tan a treated animal

12、hide to produce leather. Ion exchange is one of the most effective techniques for the removal of chromium from tannerywastewaters. Chromium exists in two stable oxidation states, Cr(III) and Cr(VI). The Cr(VI) state is of particular concern because this form is hazardous to health. Chromium is intro

13、duced into natural bodies of water from industries such as electroplating, leather tanning, cement, steel and photography. It is found in solution in different chemical forms, for example, textile and tanning wastes may contain either the hexavalent or trivalent chromium species, while electroplatin

14、g and metal finishing wastes contain primarily the trivalent chromium species. Cadmium is one of the most toxic heavy metals and is considered non-essential for living organisms. This element is found at low concentrations in natural environments, but human activities have led to increased levels on

15、 all the continents. Cadmium is present in wastewaters from metallurgical alloying, ceramics, electroplating, photography, pigment works, textile printing, chemical industries and lead mine drainage. Cadmium is removed from wastewaters by precipitation, electrocoagulation, adsorption, biosorption, a

16、ctivated carbon filtration and ion exchange. Amberlite IR 120 is a gel-type polystyrene, sulphonated strong cation-exchange resin. Rohm and Haas 24 showed that its principal characteristics have excellent physical, chemical and thermal stability, good ion-exchange kinetics and high exchange capacity

17、. Conservative technologies for metal control have an increasing interest, as they are able to remove pollutants and reuse valuable by-products obtained from wastes and/or side streams from manufacturing processes. The present paper examines optimum conditions of a strong cation- exchange resin (Amb

18、erlite IR 120) for the removal and recovery of chromium and cadmium.2. Material and methods2:1. Reagents, solutions, resins and equipmentThe resin used in this work was Amberlite IR 120 (Rohm and Haas Company), a strong acidic cation-exchange resin based on a styrene matrix. Table 1 shows the main p

19、hysicochemical properties of the resin investigated, and Table 2 shows suggested operational conditions of the resin. This resin was prepared in two different cationic forms as Na + and H +. Under these two conditions, exchange capacities, moisture content and other optimum conditions were determine

20、d in a batch system.The optimum conditions were concentration, pH, stirring time and resin amount. Chromium and cadmium amounts were determined by atomic absorption spectrophotometry (AAS) on a Model Spect. AA 20 (Varian) with an airacetylene flame used for determination of the chromium amounts in t

21、he aqueous phase with the following settings: wavelength, 357.9; lamp current, 7 mA; slit, 0.2 nm; air/acetylene ratio, 3.5/1.5; and for cadmium with the following settings: wavelength, 228.8; lamp current, 4 mA; slit, 0.5 nm; air/acetylene ratio, 3.5/1.5. All pH measurements were made with a pH-met

22、er (Metrohm) and a combination glass electrode.Analytical reagent-grade basic chromic sulphate Cr4(SO4)5(OH)2, Cd(NO3) 2. 4H20, HCI, NaCI NaOH, and chemicals (Merck, Germany) were used. Freshly prepared solutions were used throughout the experiments. Water was deionized and purified further with a M

23、illi-Q water purification system (Millipore, USA).Table 1Physicochemical properties of the Amberlite IR 120 resinFunctional group Sulphonic Matrix Styrene Moisture-holding capacity, %: Na + form 44-49 H + form 41-56Total exchange capacity, eq/L: Na form 2.00 H form 1.80Table 2Suggested operating con

24、ditions of Amberlite IR 120Operation temperature, C 120 max. Service flow rate, BV/h 5-40 Regenerants HC1、H2SO4 、NaCI Flow rate, bed volume/h 2-8 2-20 2-8 Concentration, % 5-8 0.7-6 10 Level, g/L 50-150 60-240 80-250 Slow rinse, BV at 2 regeneration flow rate Fast rinse, BV at service 4-8flow rate2.

25、2. Procedures2.2.1. Conditioning of resinAfter three preliminary recyclings of the resin in a column system with 1M HC1 and NaOH solutions to remove eventual chemical residues (solvents, functionalizing agents) trapped in the matrixes of the resins during their preparation, the samples were finally

26、converted into sodium and hydrogen forms by 1 M NaCl or HCl.2.2.2. Determination of the resin moisture content Samples of 1 g of ion exchangers in the Na and H + forms were dried at 110C for 1 h, cooled in a desiccator and weighed. This was continued until the attainment of a constant weight.2.2.3.

27、Determination of ion-exchange capacity The ion-exchange capacity was determined in reference to both Na and H forms by using column techniques. Accordingly, after loading the sample (3g) into a glass column, the resin was eluted with 20 mg L -1 concentration of chromium and cadmium solutions at a 2

28、BV/h flow rate. The results are given in Table 3 with determined moisture contents.Table 3Exchange capacities and moisture content of the resinResin (Amberlite IR 120) Na form H form Capacity (eq/L) (column) 1.12 0.97 Capacity(eq/L) (titrimetric) 1.47 1.36 Moisture content (%) 47.45 55.202.2.4. Gene

29、ral study procedure The conditioned resin samples (Na + and H forms) were used for removal of chromium and cadmium in the batch method. The effects of concentration, pH, stirring time and resin amount were investigated for determination of optimum conditions. An amount of 0.1 g resin samples was put

30、 into contact with 50 mL of solution containing chromium and cadmium for 20 min (pH 5). Stirring speed was 2000 rpm during the batch experiments. All the operations were conducted at room temperature. After filtration of the solid phase, the content of chromium and cadmium in the liquid phase were d

31、etermined by AAS.3. Results3.1. Operating conditions for the Amberlite IR 120 resin 3.1.1. ConcentrationChromium(III) and cadmium(II) concentrations were selected in the range of 2 to 50 mg/L for two different ionic forms of resin (studied pH: 5.5). The effect of concentration on metal adsorption wa

32、s investigated and the results are given in Figs. 1 and 2. Experiments were done using 0.1 g of resin with different metal concentrations (2- 50 rag/L). It was found that the metal amounts retained were almost stable in this concentration range for both the metal and ionic forms of resin. Adsorption of cadmium was a bit higher than chromium for both forms of this resin. In the beginning values of concentration, the results show that there was higher adsorption of the Na + form. The maximum adsorption was obtained as 93.4% for cadmium and 90.27% for chromiu