Regeneration of Anionic Exchange Resin Used in Hexavalent Chromate Removal

Transcription

1 Vol. XXXXII 2014 ISSN JPIChE 42 (2) 2014: Journal of Pakistan Institute of Chemical Engineers Journal of The Pakistan Institute of Chemical Engineers journal homepage: Regeneration of Anionic Exchange Resin Used in Hexavalent Chromate Removal M. A. Ashraf,W. A. Khan, M. Zia ul haq, S. Muhammad, K. Shahzad, J. R. Khan Submitted: 08/07/2014, Accepted: 11/09/2014, Online: 09/12/2014 Abstract Chromium based compounds have extensive use in many industries like chrome tanning and electrochemical +6 industries. Chromate ions (especially hexavalent; Cr ) are toxic pollutants, as they are carcinogenic in nature, it is necessary to remove them from industrial waste water. Different methods have been employed for the removal of highly toxic chromium from effluents. These methods include chemical process, electrochemical process and ion exchange process. These methods work under two categories; some of them reduce hexavalent chromium to trivalent and then separates it and some remove hexavalent chromium as insoluble chromates or dichromates. Present work is being undertaken to produce regeneration data for parameters like flow rate, concentration of the solution passed through resin bed and temperature using an anionic exchanger (Purolite A-400) after chromate removal. Atomic absorption spectrometer (Z-8200) used for the measurement of chromium concentration in resin. +6 Key Words: Hexavalent Cr, Purolite A-400 Introduction: Ion exchange process deals with different metals and ionized organic compounds removal by passing the waste stream through a resin bed, similar charge ions are removed from the resin surface in exchange of ions present in solution. After exhaustion the resin can be regenerated by passing a concentrated solution containing the original ion through the resin bed. The resin is selected according to the nature of ions present in solution either cations or anions. Resins used in ion exchange process are insoluble substances containing ions which are exchangeable with other ions present in solutions when come in 1 Department of Chemical Engineering, NFC IE&FR, Faisalabad. 2 Centre for Coal Technology, University of the Punjab, Lahore 3 Department of Chemical Engineering, UET, Lahore contact with them. Ion exchange resin remains physically stable during exchange of ions. Ion exchange resins are insoluble in nature and may contain acids or bases as functional group, and this functional group enables resin to exchange either positively charged ions (cation exchange resins) or negatively charged (anion exchange resins). Soil particles, proteins and living cells are natural substances which have ion exchange properties and play an important role in nature. The ion exchange process has many advantages which include long resin life, reuse of resin after regeneration and low maintenance charges etc. In addition, this is environmental friendly process and Corresponding Author: Mohammad Awais Ashraf. (moawas@gmail.com) 119

2 120 Journal of the Pakistan Institute of Chemical Engineers Vol. XXXXII deals only with salts and metals present in solution. Resin Classification i) Strong base anion resins ii) Weak-base anion resins iii) Strong-acid cation resin iv) Weak-acid cation resins v) Heavy-metal selective chelating resins Ion exchange resins are classified based on the type of functional group they contain Strong base Anion exchange resin: SBA has extensive use for removal of metals and other contaminants from drinking and waste water. Many applications require special resins: for examples Removal of heavy metals from waste water: Cadmium, Chromium, Iron, Mercury, Nickel and Zinc. Boron removal from drinking water Nitrate removal from drinking water Perchlorate removal from drinking water Purolite A400 is strong-base anion exchanger and its operating capacity is high. Minimal quantities of sodium chloride are required as compared to (Purolite A600) based on polystyrene quaternary ammonium structure. Its structure is gel type and regeneration efficiency is also high. Purolite A400 has exceptional physical stability due to which it has long life without excessive pressure drop; its kinetics of exchange is also good. Regeneration of an ion exchange resin: Regeneration of exhausted resin starts when mostly ions have been replaced from the resin by the ions that we want to recover from the solution. We can bring exhausted resin back to the fresh state and again use it. That why resin regeneration is a reverse of the exchange process. In Industry an ion-exchange resin is regenerated after every 12 to 36 hours depending its load. Different regenerants can be used for regeneration of exhausted resin in different ways depending on its use. Regenerants Selection: Regenerants are selected according to the nature of resin and the functional group attached to the resin. Regeneration can only be performed when the concentration of the regenerants is high. In our case, the resin is regenerated with salt (common salt: NaCl) solution. Regeneration of anion - exchanger having ionic form Cl is influenced by the NaCl. Experimental Setup: Experiments have been performed on exhausted ion exchange resin which include the following objectives; 1. To minimize the cost of chromate removal process by reusing the regenerated resin bed. 2. To find the %age regeneration of the resin bed by using different regenerants concentration and operating conditions. An experimental setup of an ion exchange column was developed at laboratory scale as shown in figure No.01.Its schematic flow diagram for the regeneration of exchange resin column is given in 3 fig # 04.The volume of resin column is 18cm and contains 19.5 g mass on moist basis. Column having internal diameter 1.4cm and cross sectional area 1.53cm2.The exhausted resin Purolite A-400 has 1.3eq/L ion exchange capacity. The specification sheet of Purolite A-400 is given in Appendix A. In this experiment a rotameter ranges (0-65) LPH used to control flow rate of regenerants.a small scale pump was installed for maintaining constant flow rate of regenerants.atomic Absorption analysis technique was employed for measuring the concentration of chromium from the anionic exchange resin

3 2014 M. A. Ashraf, W. A. Khan, M. Zia ul haq, S. Muhammad, K. Shahzad, J. R. Khan 121 Fig. 2: Schematic flow diagram for the regeneration of exchange resin column Fig. 1: Experimental setup of an ion exchange Experimentation Methodology: The rotameter used for flow rate A numbers of experiments were performed to find measurements in the experiment. the %age regeneration of the anion exchange resin Kept the regenerant concentration b/w bed by using different regenerants concentration 0.5-6M. and operating conditions. o Kept the temperature range b/w C In this study NaCl solution made in distilled water Kept the flow rate range b/w L/hr was used. For hexavalent chromate containing The different categories of experiments include; anionic resin (A-400) NaCl solution in distilled water will give better response as regenerant. Category 1: Because NaCl solutions made in tap and ground waters contain impurities (tap water is chlorinated water) and different salts (Ground water is permanent hard water containing many salts). Filling up the exchange column with exhausted resin supported by beads bed. NaCl solution introduced into the column with a small scale pump. In this category, keeping volumetric flow rate, temperature and mass of resin constant regenerant (NaCl solution) of different concentration was prepared in distilled water and then passed through the exhausted resin bed. In this category I performed twelve experiments. Category 2: In this category, keeping volumetric flow rate, mass

4 122 Journal of the Pakistan Institute of Chemical Engineers Vol. XXXXII of resin and concentration of regenerant (NaCl Performance Calculations: Solution) constant experiments were performed by Laboratory Column data for Calculations: passing regenerants at different temperatures Initial concentration of Chromium in exhausted through exhausted resin. I performed six resin=35.34 ppm experiments in this category. Regenerant volume=5l Category 3: Resin volume = 18cm 3 In this category, keeping temperature and mass of the resin constant different flow rates of regenerant (NaCl solution) having same concentration were passed through exhausted resin. I performed five experiments were performed in this category. Resin mass =19.5g (on moist basis). Column Internal diameter =1.4cm Column Length =50 cm. Rotameter = (0-65) l/hr. For measuring the concentration from the anionic exchanger Atomic Absorption analysis technique was employed Category 1: Changing concentrations of NaCl solution while keeping volumetric flow rate, temperature and mass of resin bed constant. Fig. 3: Cr. Concentration in resin Ppm Vs NaCl Concentration (Molarity) Fig. 4: %age regeneration Vs NaCl Concentration (Molarity)

5 2014 M. A. Ashraf, W. A. Khan, M. Zia ul haq, S. Muhammad, K. Shahzad, J. R. Khan 123 Category 2: Changing regenerants temperatures keeping volumetric flow rate, mass of resin bed and concentration of Solution constant. Fig. 6: %age regeneration Vs Flow Rate (l/hr) Fig. 5: Cr. Concentration in resin (ppm) Vs Temperature ( C) Conclusions: Experiments under the category 1 showed that regeneration of resin is increasing by increasing regenerant concentration and is maximum with 5 M solution. Experiments of category 2 gave considerably good results for increase in regenerant temperature and showed that temperature also effects regeneration. 0 Resin is best regenerated at 55 C. Category 3 experiments showed 6.5 l/hr be the best volumetric flow for the good results for the regeneration of resin. References: 1. Mackenziel David, David A cornwell, Fig. 6: %age regeneration Vs Temperature ( C) introduction to environmental engineering th 4 edition; PP Category 3: 2. Coulson & Richardson, Chemical Changing flow rate of regenerant while keeping nd concentration, temperature and mass of the resin engineering, 2 edition, pp bed constant. 3. Kirk Othmer; Encyclopedia of chemical Fig. 7: Cr. Concentration in resin (ppm) Vs Flow Rate (l/hr) technology volume 13, Ion Exchange (Wiley, New york, 1981). 4. Schewitzer, P.A, Handbook of separation techniques for Chemical Engineers, 2nd edition (McGraw-Hill, New York, 1988). 5. Sofia A. Cavaco, Sandra Fernandes, Removal of chromium from electroplating industry effluents by ion exchange resins Engineering Department, University of Coimbra, Portugal, Journal of Hazardous Materials Volume 144, Issue 3, 18 June 2007.

6 124 Journal of the Pakistan Institute of Chemical Engineers Vol. XXXXII 6. Silke Karcher, Anja Kornmüller, Anion anion exchangers Issue Journal of Applied exchange resins for removal of reactive dyes Polymer Science Volume 86, Issue 8, pages from textile wastewaters, Department of , 21 November Water Quality Control, Germany, Water 12. S. Mustafa, H. Bashir, Selectivity reversal Research Volume 36, Issue 19, November and dimerization of chromate in the exchanger Amberlite IRA-400 National 7. a, b J M. Tobin, J C. Roux chromium removal Centre of Excellence in Physical Chemistry, from tanning effluent Water Research University of Peshawar, Peshawar, Volume 32, Issue 5, 1 March Pakistan. Reactive and Functional Polymers 8. a, b Violeta Neagu, I. Untea, Retention of Volume 34, Issues 23, November chromate ion by conventional and N- 13. T. V. Arden, M. Giddings Anion exchange in ethylpyridinium strongly basic anion chromate solution Journal of Applied exchange resins Reactive and Functional Chemistry Volume 11, Issue 7, pages Polymers Volume 57, Issues 23, December ,Article 4, MAY S Yalcin, R Apak, J Hizal, Recovery Of Copper (ii) And Chromium (iii,vi) From Electroplating-industry Wastewater By Ion Exchange Separation Science and Technology Volume 36, Issue 10, Penny Woodberry, Geoff Stevens Removal of Metal Contaminants by Ion-Exchange Resin Columns, Antarctica, Solvent Extraction and Ion Exchange Volume 24, Issue 4, I. Untea, Elena Tudorache, Cr(VI)- containing wastewater treatment by means of ion exchange on weak- and strong-base