Effluents from the copper electrorefining as a secondary source of antimony: Role of mass transfer on the recovery by electrodeposition

The limited availability of antimony has increased the need for exploiting alternative sources to its direct extraction from stibnite deposits. Furthermore, introducing recovery techniques in industries where antimony is released in wastewaters leads to more responsible production routes. In this work, electrodeposition is employed to recover the antimony present in a secondary waste effluent of the copper electrorefining that is highly concentrated in hydrochloric acid. The electrochemical characterization of the system was conducted by voltammetry to identify a range of suitable operating conditions for the potentiostatic and galvanostatic electro-recovery of antimony. In potentiostatic mode, the progress of the secondary electrode reactions of hydrogen and chlorine evolution at potentials more cathodic than −0.38 V vs. Ag/AgCl causes the detachment and redissolution of the deposited antimony. Operating under galvanostatic control, similar effects were observed when the limiting current density is exceeded. Current efficiency and specific energy consumption values above 50 % and below 65 kW·h·kg−1, were achieved below the limiting current density (1.265 mA·cm−2). The operational range where electrodeposition of antimony is accelerated at increasing current densities can be broadened at intensified hydrodynamic conditions and higher concentrations of antimony. The detrimental effect of the hydrogen evolution reaction on the recovery of antimony decreases at high HCl concentrations

ZnO/ZnS heterostructures for hydrogen production by photoelectrochemical water splitting

This work studies the photoelectrochemical behavior of novel ZnO/ZnS heterostructures obtained by means of anodization in water and glycerol/water/NH4F electrolytes with different Na2S additions under controlled hydrodynamic conditions. For this purpose different techniques such as Field Emission Scanning Electronic Microscopy (FE-SEM) with EDX, Raman spectroscopy and photoelectrochemical water splitting tests under standard AM 1.5 conditions have been carried out. The obtained results showed that the hydrodynamic conditions promoted an ordered nanotubular morphology which facilitates electron-hole separation and consequently, the photoelectrochemical activity for water splitting is enhanced. Additionally, the effect of glycerol in the anodization solutions seems to be beneficial for increasing the dark current photostability

Voltammetric and electrodeposition study for the recovery of antimony from effluents generated in the copper electrorefining process

Antimony is a metalloid with limited availability as a primary resource, but it is commonly found as an impurity in effluents generated in the copper metallurgy. Thus, the development of clean and selective processes to recover antimony from these wastewaters would improve the sustainability of the copper production. In this work, an emulated effluent of the copper electrorefining industry that contains antimony and hydrochloric acid was characterized by means of voltammetric and electrodeposition tests using two different cell configurations: a static cell, and a dynamic cell with a rotating disk electrode (RDE). Voltammograms were obtained at varying hydrochloric acid and antimony concentrations, inversion potentials, scan rates and RDE rotation rates. Two main conclusions were drawn: (a) the deposition of antimony is a mass transfer-controlled process; and (b) an increase in hydrochloric acid concentration improves the deposition of antimony. The diffusion coefficient of antimony species was obtained applying the Randles-ˇ Sevˇcík and the Levich equations; both of them providing very similar values (5.29 ± 0.20 ⋅ 10− 6 cm2 s − 1). The effective electrodeposition of antimony from highly concentrated hydrochloric acid solutions was demonstrated. The surface examination of the electrodes revealed that compact and adherent deposits of antimony could be obtained under operating conditions that minimize the hydrogen evolution reaction in both potentiostatic and galvanostatic modes. Intensified convective regimes by using the RDE improve the supply of dissolved antimony towards the electrode surface, thus leading to a notorious increase in current density and, consequently, in the rate of antimony deposition

Enhanced Atenolol oxidation by ferrites photoanodes grown on ceramic SnO2-Sb2O3 anodes

The increase in the consumption of pharmaceutical compounds has caused the increment of their presence in different body waters. β-blockers are one of the most dangerous even at low concentrations (ng L−1). Anodic oxidation with a boron-doped diamond (BDD) anode presents good results to remove these compounds. However, since this anode is expensive, some cheaper materials are under study. In this work, Sb-doped SnO2 ceramic anodes (BCE) coated with Zn or Cd ferrites, in order to provide photocatalytic properties, have been applied to the degradation of the Atenolol (ATL) β-blocker. Increasing the applied current increased ATL degradation and mineralization but caused a decrease in mineralization current efficiency (MCE) and an increase in energy consumption (ETOC). Additionally, light irradiation enhanced the ATL mineralization rate between 10% and 20% for both ferrites, although this increase was higher for the cadmium ferrite one. Finally, when the ferrites were compared with BDD and BCE anodes, the oxidizing power of the different anodic materials can be ordered as follows BDD> Cd-Fe> Zn-Fe> BCE. Therefore, both ferrites improved the BCE performance but only the cadmium one appeared as an alternative to the BDD, especially for MCE and ETOC, reaching values of 15% and 0.5 kWh gTOC−1, respectively

Study of the chlorfenvinphos pesticide removal under different anodic materials and different reactor configuration

The present manuscript focuses on the study of the electrochemical oxidation of the insecticide Chlorfenvinphos (CVP). The assays were carried out under galvanostatic conditions using boron-doped diamond (BDD) and lowcost tin dioxide doped with antimony (Sb-doped SnO2) as anodes. The influence of the operating variables, such as applied current density, presence or absence of a cation-exchange membrane and concentration of supporting electrolyte, was discussed. The results revealed that the higher applied current density the higher degradation and mineralization of the insecticide for both anodes. The presence of the membrane and the highest concentration of Na2SO4 studied (0.1 M) as a supporting electrolyte benefited the oxidation process of CVP using the BDD electrode, while with the ceramic anode the elimination of CVP was lower under these experimental conditions. Although the BDD electrode showed the best performance, ceramic anodes appear as an interesting alternative as they were able to degrade CVP completely for the highest applied current density values. Toxicity tests revealed that the initial solution of CVP was more toxic than the samples treated with the ceramic electrode, while using the BDD electrode the toxicity of the sample increased

The effectiveness of the stabilization/solidification process on the leachability and toxicity of the tannery sludge chromium

[EN] A stabilization/solidification (S/S) process by using cement was applied to tannery sludge in order to find a safer way of landfilling this waste. The effects of three parameters on the process effectiveness were analysed in terms of leachate toxicity and chromium retention (%). The parameters studied were the relative amount of added water (30e50 wt.%), cement (10e60 wt.% in the solid components), and the use of three different types of cement (clinker with additions of limestone, with additions of limestone and fly ashes, and with additions of pozzolans). Statistical analysis performed by variance analysis and categorical multifactorial tests reveals that all the studied parameters significantly influence the effectiveness of the process. Results showed that chromium retention decreases as the relative amount of cement and water increases, probably due to additional chromium provided by cement and increased in the porosity of the mixtures. Leachate toxicity showed the same minimum value for mixtures with 30% or 40% cement, depending on the type of cement, showing that clinker is the main material responsible for the process effectiveness, and additives (pozzolans or fly ashes) do not improve it. The volume increase is lower as less sludge is replaced by cement and the relative amount of water decreases, and for the cement without additions of fly ashes or pozzolans. Therefore, the latter seems to be the most appropriate cement in spite of being more expensive. This is due to the fact that the minimum toxicity value is achieved with a lower amount of cement; and moreover, the volume increase in the mixtures is lower, minimizing the disposal cost to a landfill.The authors wish to express their gratitude to the tannery facility INCUSA, S.A., to the cement facility CEMEX ESPAÑA, S.A. and to Carles Martínez for his translation assistance.Montañés Sanjuan, MT.; Sánchez Tovar, R.; Roux, MSB. (2014). The effectiveness of the stabilization/solidification process on the leachability and toxicity of the tannery sludge chromium. Journal of Environmental Management. 143:71-79. doi:10.1016/j.jenvman.2014.04.026S717914

Analysis of norfloxacin ecotoxicity and the relation with its degradation by means of electrochemical oxidation using different anodes

[EN] In this work, ecotoxicological bioassays based on Lactuca sativa seeds and bioluminescent bacterium (Vibrio fischeri) have been carried out in order to quantify the toxicity of Norfloxacin (NOR) and sodium sulfate solutions, before and after treating them using electrochemical advanced oxidation. The effect of some process variables (anode material, reactor configuration and applied current) on the toxicity evolution of the treated solution has been studied. A NOR solution shows an EC50 (5 days) of 336 mg L-1 towards Lactuca sativa. This threshold NOR concentration decreases with sodium sulfate concentration, in solutions that contain simultaneously Norfloxacin and sodium sulfate. In every case considered in this work, the electrochemical advanced oxidation process increased the toxicity (towards both Lactuca sativa and Vibrio fischeri) of the solution. This toxicity increase is mainly due to the persulfate formation during the electrochemical treatment. From a final solution toxicity point of view, the best results were obtained using a BDD anode in a divided reactor applying the lowest current intensity.The authors are very grateful to the Ministerio de Economia y Competitividad (Projects CTQ2015-65202-C2-1-R and RTI2018-101341-B-C21) for their economic support.Montañés, M.; García Gabaldón, M.; Roca-Pérez, L.; Giner-Sanz, JJ.; Mora-Gómez, J.; Pérez-Herranz, V. (2020). Analysis of norfloxacin ecotoxicity and the relation with its degradation by means of electrochemical oxidation using different anodes. Ecotoxicology and Environmental Safety. 188:1-10. https://doi.org/10.1016/j.ecoenv.2019.109923S110188Banks, M. K., & Schultz, K. E. (2005). Comparison of Plants for Germination Toxicity Tests in Petroleum-Contaminated Soils. Water, Air, and Soil Pollution, 167(1-4), 211-219. doi:10.1007/s11270-005-8553-4Barreto, J. P. d. P., Araujo, K. C. d. F., de Araujo, D. M., & Martinez-Huitle, C. A. (2015). Effect of sp3/sp2 Ratio on Boron Doped Diamond Films for Producing Persulfate. ECS Electrochemistry Letters, 4(12), E9-E11. doi:10.1149/2.0061512eelBueno, F., Borba, F. H., Pellenz, L., Schmitz, M., Godoi, B., Espinoza-Quiñones, F. R., … Módenes, A. N. (2018). Degradation of ciprofloxacin by the Electrochemical Peroxidation process using stainless steel electrodes. Journal of Environmental Chemical Engineering, 6(2), 2855-2864. doi:10.1016/j.jece.2018.04.033Carlesi Jara, C., Fino, D., Specchia, V., Saracco, G., & Spinelli, P. (2007). Electrochemical removal of antibiotics from wastewaters. Applied Catalysis B: Environmental, 70(1-4), 479-487. doi:10.1016/j.apcatb.2005.11.035Charles, J., Crini, G., Degiorgi, F., Sancey, B., Morin-Crini, N., & Badot, P.-M. (2013). Unexpected toxic interactions in the freshwater amphipod Gammarus pulex (L.) exposed to binary copper and nickel mixtures. Environmental Science and Pollution Research, 21(2), 1099-1111. doi:10.1007/s11356-013-1978-1Chen, M., & Chu, W. (2012). Degradation of antibiotic norfloxacin in aqueous solution by visible-light-mediated C-TiO2 photocatalysis. Journal of Hazardous Materials, 219-220, 183-189. doi:10.1016/j.jhazmat.2012.03.074Coledam, D. A. C., Aquino, J. M., Silva, B. F., Silva, A. J., & Rocha-Filho, R. C. (2016). Electrochemical mineralization of norfloxacin using distinct boron-doped diamond anodes in a filter-press reactor, with investigations of toxicity and oxidation by-products. Electrochimica Acta, 213, 856-864. doi:10.1016/j.electacta.2016.08.003Da Silva, S. W., Navarro, E. M. O., Rodrigues, M. A. S., Bernardes, A. M., & Pérez-Herranz, V. (2019). Using p-Si/BDD anode for the electrochemical oxidation of norfloxacin. Journal of Electroanalytical Chemistry, 832, 112-120. doi:10.1016/j.jelechem.2018.10.049Davis, J., Baygents, J. C., & Farrell, J. (2014). Understanding Persulfate Production at Boron Doped Diamond Film Anodes. Electrochimica Acta, 150, 68-74. doi:10.1016/j.electacta.2014.10.104Oliveira, G. A. R. de, Leme, D. M., de Lapuente, J., Brito, L. B., Porredón, C., Rodrigues, L. de B., … Oliveira, D. P. de. (2018). A test battery for assessing the ecotoxic effects of textile dyes. Chemico-Biological Interactions, 291, 171-179. doi:10.1016/j.cbi.2018.06.026Drèze, V., Monod, G., Cravedi, J.-P., Biagianti-Risbourg, S., & Le Gac, F. (2000). Ecotoxicology, 9(1/2), 93-103. doi:10.1023/a:1008976431227Flaherty, C. M., & Dodson, S. I. (2005). Effects of pharmaceuticals on Daphnia survival, growth, and reproduction. Chemosphere, 61(2), 200-207. doi:10.1016/j.chemosphere.2005.02.016González-Pleiter, M., Gonzalo, S., Rodea-Palomares, I., Leganés, F., Rosal, R., Boltes, K., … Fernández-Piñas, F. (2013). Toxicity of five antibiotics and their mixtures towards photosynthetic aquatic organisms: Implications for environmental risk assessment. Water Research, 47(6), 2050-2064. doi:10.1016/j.watres.2013.01.020Gustavson, K. E., Sonsthagen, S. A., Crunkilton, R. A., & Harkin, J. M. (2000). Groundwater toxicity assessment using bioassay, chemical, and toxicity identification evaluation analyses. Environmental Toxicology, 15(5), 421-430. doi:10.1002/1522-7278(2000)15:53.0.co;2-zHeberle, A. N. A., Alves, M. E. P., da Silva, S. W., Klauck, C. R., Rodrigues, M. A. S., & Bernardes, A. M. (2019). Phytotoxicity and genotoxicity evaluation of 2,4,6-tribromophenol solution treated by UV-based oxidation processes. Environmental Pollution, 249, 354-361. doi:10.1016/j.envpol.2019.03.057Iniesta, J. (2001). Electrochemical oxidation of phenol at boron-doped diamond electrode. Electrochimica Acta, 46(23), 3573-3578. doi:10.1016/s0013-4686(01)00630-2Larsson, D. G. J., de Pedro, C., & Paxeus, N. (2007). Effluent from drug manufactures contains extremely high levels of pharmaceuticals. Journal of Hazardous Materials, 148(3), 751-755. doi:10.1016/j.jhazmat.2007.07.008Leme, D. M., & Marin-Morales, M. A. (2009). Allium cepa test in environmental monitoring: A review on its application. Mutation Research/Reviews in Mutation Research, 682(1), 71-81. doi:10.1016/j.mrrev.2009.06.002Li, Y., Niu, J., & Wang, W. (2011). Photolysis of Enrofloxacin in aqueous systems under simulated sunlight irradiation: Kinetics, mechanism and toxicity of photolysis products. Chemosphere, 85(5), 892-897. doi:10.1016/j.chemosphere.2011.07.008Liu, P., Zhang, H., Feng, Y., Yang, F., & Zhang, J. (2014). Removal of trace antibiotics from wastewater: A systematic study of nanofiltration combined with ozone-based advanced oxidation processes. Chemical Engineering Journal, 240, 211-220. doi:10.1016/j.cej.2013.11.057Mao, F., He, Y., & Gin, K. (2018). Evaluating the Joint Toxicity of Two Benzophenone-Type UV Filters on the Green Alga Chlamydomonas reinhardtii with Response Surface Methodology. Toxics, 6(1), 8. doi:10.3390/toxics6010008Mora-Gómez, J., García-Gabaldón, M., Ortega, E., Sánchez-Rivera, M.-J., Mestre, S., & Pérez-Herranz, V. (2018). Evaluation of new ceramic electrodes based on Sb-doped SnO2 for the removal of emerging compounds present in wastewater. Ceramics International, 44(2), 2216-2222. doi:10.1016/j.ceramint.2017.10.178Mora-Gomez, J., Ortega, E., Mestre, S., Pérez-Herranz, V., & García-Gabaldón, M. (2019). Electrochemical degradation of norfloxacin using BDD and new Sb-doped SnO2 ceramic anodes in an electrochemical reactor in the presence and absence of a cation-exchange membrane. Separation and Purification Technology, 208, 68-75. doi:10.1016/j.seppur.2018.05.017Özcan, A., Atılır Özcan, A., & Demirci, Y. (2016). Evaluation of mineralization kinetics and pathway of norfloxacin removal from water by electro-Fenton treatment. Chemical Engineering Journal, 304, 518-526. doi:10.1016/j.cej.2016.06.105Priac, A., Badot, P.-M., & Crini, G. (2017). Treated wastewater phytotoxicity assessment using Lactuca sativa : Focus on germination and root elongation test parameters. Comptes Rendus Biologies, 340(3), 188-194. doi:10.1016/j.crvi.2017.01.002Radix, P., Léonard, M., Papantoniou, C., Roman, G., Saouter, E., Gallotti-Schmitt, S., … Vasseur, P. (2000). Comparison of Four Chronic Toxicity Tests Using Algae, Bacteria, and Invertebrates Assessed with Sixteen Chemicals. Ecotoxicology and Environmental Safety, 47(2), 186-194. doi:10.1006/eesa.2000.1966Rizzo, L. (2011). Bioassays as a tool for evaluating advanced oxidation processes in water and wastewater treatment. Water Research, 45(15), 4311-4340. doi:10.1016/j.watres.2011.05.035Seco, J. I., Fernández-Pereira, C., & Vale, J. (2003). A study of the leachate toxicity of metal-containing solid wastes using Daphnia magna. Ecotoxicology and Environmental Safety, 56(3), 339-350. doi:10.1016/s0147-6513(03)00102-7Uzu, G., Sobanska, S., Sarret, G., Muñoz, M., & Dumat, C. (2010). Foliar Lead Uptake by Lettuce Exposed to Atmospheric Fallouts. Environmental Science & Technology, 44(3), 1036-1042. doi:10.1021/es902190uVasconcelos, T. G., Henriques, D. M., König, A., Martins, A. F., & Kümmerer, K. (2009). Photo-degradation of the antimicrobial ciprofloxacin at high pH: Identification and biodegradability assessment of the primary by-products. Chemosphere, 76(4), 487-493. doi:10.1016/j.chemosphere.2009.03.022Wang, W. C., & Freemark, K. (1995). The Use of Plants for Environmental Monitoring and Assessment. Ecotoxicology and Environmental Safety, 30(3), 289-301. doi:10.1006/eesa.1995.1033Wang, X., Sun, C., Gao, S., Wang, L., & Shuokui, H. (2001). Validation of germination rate and root elongation as indicator to assess phytotoxicity with Cucumis sativus. Chemosphere, 44(8), 1711-1721. doi:10.1016/s0045-6535(00)00520-8Yang, L.-H., Ying, G.-G., Su, H.-C., Stauber, J. L., Adams, M. S., & Binet, M. T. (2008). GROWTH-INHIBITING EFFECTS OF 12 ANTIBACTERIAL AGENTS AND THEIR MIXTURES ON THE FRESHWATER MICROALGA PSEUDOKIRCHNERIELLA SUBCAPITATA. Environmental Toxicology and Chemistry, 27(5), 1201. doi:10.1897/07-471.1Yuan, F., Hu, C., Hu, X., Wei, D., Chen, Y., & Qu, J. (2011). Photodegradation and toxicity changes of antibiotics in UV and UV/H2O2 process. Journal of Hazardous Materials, 185(2-3), 1256-1263. doi:10.1016/j.jhazmat.2010.10.040Zhou, Y., Xu, Y.-B., Xu, J.-X., Zhang, X.-H., Xu, S.-H., & Du, Q.-P. (2015). Combined Toxic Effects of Heavy Metals and Antibiotics on a Pseudomonas fluorescens Strain ZY2 Isolated from Swine Wastewater. International Journal of Molecular Sciences, 16(2), 2839-2850. doi:10.3390/ijms16022839Zhu, L., Santiago-Schübel, B., Xiao, H., Hollert, H., & Kueppers, S. (2016). Electrochemical oxidation of fluoroquinolone antibiotics: Mechanism, residual antibacterial activity and toxicity change. Water Research, 102, 52-62. doi:10.1016/j.watres.2016.06.00

Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

[EN] This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25-60°C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest iG values at 60°C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H3PO4 media from a corrosion point of view for all the temperatures analysedThe authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/8196/07, C/018046/08, D/023608/09) and to Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; García Antón, J.; Guenbour, A.; Ben Bachir, A. (2011). Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures. Corrosion Science. 53(4):1237-1246. https://doi.org/10.1016/j.corsci.2010.12.017S1237124653

Effects of microplasma arc AISI 316L welds on the corrosion behaviour of pipelines in LiBr cooling systems

[EN] The effect of microplasma arc welding (MPAW) on the electrochemical and corrosion behaviour of AISI 316L stainless steel tubes has been studied. Scanning electrochemical measurements were performed in sodium chloride to evaluate the difference in the electrochemical activity of base (non-welded) and welded samples. Oxygen reduction rates increase in AISI 316L due to the heat treatment effect induced by welding, indicating a higher electrochemical activity in the welded samples. Additionally, the use of MPA weldments in lithium bromide (LiBr) absorption machines was also analysed at typical operating temperatures and Reynolds numbers. The welding process increases corrosion rates, hinders passivation and increases the susceptibility to pitting attack in LiBr. However, zero-resistance ammeter and localization index measurements show that the galvanic pair generated between the base and welded alloys is weak, both electrodes being in their passive state. Temperature greatly affects the corrosion process. (C) 2013 Elsevier Ltd. All rights reserved.The authors would like to express their gratitude to the FPU grant given to Rita Sanchez Tovar, MICINN (CTQ2009-07518), to FEDER, to the Programa de Apoyo a la Investigacion y Desarrollo de la UPV (PAID-06-11-1864), to the Generalitat Valenciana for its help in the SECM acquisition (PPC/2011/013) and to Dr. Asuncion Jaime for her translation assistance.Sánchez-Tovar, R.; Montañés, M.; García-Antón, J. (2013). Effects of microplasma arc AISI 316L welds on the corrosion behaviour of pipelines in LiBr cooling systems. Corrosion Science. 73:365-374. https://doi.org/10.1016/j.corsci.2013.04.025S3653747

Effects of flow variations on the galvanic corrosion of the copper/AISI 304 stainless steel pair in lithium bromide using a zero-resistance ammeter

[EN] The effects of flow variations on the galvanic corrosion of the copper/AISI 304 stainless steel pair in a concentrated lithium bromide solution were investigated in a hydraulic circuit applying different flow steps and using a zero-resistance ammeter (ZRA). The flow steps consist in applying a flow rate for sixty minutes after leaving the system under stagnant conditions for another sixty minutes; this procedure is repeated during eight hours. The magnitude of the steps is different depending on the flow regime studied, ranging from a Reynolds number of 633 to 5066. Results show that, when a flow step is applied, the galvanic current density increases and the galvanic potential shifts towards more negative values. However, with time, this increase in the galvanic current density is lower, reaching its lowest value in the last hour of the experiment at a Reynolds number of 5066. Thus, although the corrosion rate increases as Reynolds number increases, the protective corrosion products are generated earlier on the copper surface. © 2012 by ESG.The authors would like to express their gratitude to the MICINN for the financial support (project CTQ2009-07518), to the FPU grant given to Rita Sánchez Tovar, to FEDER (Fondo Europeo de Desarrollo Regional) and to Dr. Asunción Jaime for her translation assistance.Montañés Sanjuan, MT.; Sánchez Tovar, R.; García Antón, J.; Pérez-Herranz, V. (2012). Effects of flow variations on the galvanic corrosion of the copper/AISI 304 stainless steel pair in lithium bromide using a zero-resistance ammeter. INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE. 7:747-759. http://hdl.handle.net/10251/31148S747759