A potentiometric stripping analysis of copper applicable to raw waste streams from common metals

plating industry is described. Glassy carbon is employed as the working electrode. The possible reactions

that would take place during the stripping process are discussed. It has been possible to estimate

less than I ppm of Cu by this method and it is free from interference by other metallic impurities present

in common metal plating effluent

Gomathi, H.

Prabhakararao, G.

IR@CECRI

Bulletin of Electrochemistry 2(6) November-December 1986, 587-589 A SIMPLE POTENTIOMETRIC STRIPPING METHOD FOR COPPER IN PLATING WASTE H GOMATHZ and G PRABHAKARA RAO Central Electrochemical Research Institute, Karaikudi-623 006 ABSTRACl A potentiometric stripping analysis of copper applicable to raw waste streams from common metals plating industry is described. Glassy carbon is employed a s  the working electrode. The possible reac- tions that would take place during the stripping process are discussed. It has been possible to estimate less than I ppm of Cu by this method and it is free from interference by other metallic impurities pre- sent in common metal plating effluent. Key Words: Potentiometric stripping analysis, metal  plating wastes,  copper estimation . INTRODUCTION C opper tops.the list of toxic pollutants met with in raw waste streams from common metals plating industry [ 1 1. A detailed review of anodic stripping voltammetric procedures available for copper in various composite materials has appeared in the seventies 1 . Recently poten- tiometric stripping analysis (PSA) procedure has been developed for analysing Cu, Cd, Pb, Sn, Bi, Zn,Th etc. on mercury film glassy carbon electrode (MFGCE) using Hg (11) [ 3 l  compounds or dissolved oxygen [ 4  1 as oxidants. The mechanistic aspects of this method have been dealt in detail subsequently 1 5  J . The present investigations are aimed at assess- ing the usefulness of Glassy Carbon (GC) as such as working electrode without any mercury film coated over it. Results of such PSA studies are reported and discussed here. EXPERIMENTAL A three electrode cell with GC working electrode, a platinum counter elec- trode and 1N calomel reference electrode was used. The working electrode (GC) was polished successively with 1/0, 2/0, 3/0 and 4/0 emery sheets. The solution was deaerated with nitrogen wherever necessary. The poten- tial of the working electrode was expressed with reference to IN calomel electrode. A magnetic stirrer was employed to stir the sample solution during experiment. An X-Y recorder (Rikadenki Model RW 201T) was used for recording E-t profiles. PROCEDURE The working electrode was held potentiostatically at a sufficiently negative potential for copper deposition and at the end of the stipulated-time, the potentiostatic circuitry was disconnected and potential-lime response was recorded under the same hydrodynamic conditions as for deposition. RESULTS AND DISCUSSION In Figs.1 and 2, typical potential-time curves obtained in an unbuffered medium (O.5M H2S04 - pH 2.2) and a buffered medium (0.1M HCI + O.IM NaOOCCH, pH 2.87) at  a copper concentration of 10-4M are presented. In both the media the preconcentration was carried out for 5 mins. at -700 mV. Stripping times obtained, show that time taken for com- plete stripping is nearly the same in the case of sulphuric acid and (hydrochloric acid + sodium acetate buffer). It is also of interest to note that no stripping signal was observed in acetic acid - sodium acetate buf- fer of pH 4-5. Fig.1. Potentiometric stripping curve for copper deposited from 10-4M CuS04 in H2S04 medium (pH 2.21 Preconcentration - 5 mins 2 These observations point to the fact that pH plays a very crucial role in the stripping process. Therefore, a pH 2-3 of either buffered or unbuf- fered medium is suitable. It is clear from Figs. 1 and 2 that a plateau oc- curs at the equilibrium dissolution potential of the metal and it is characteristic for each medium and also varies with the nature of the substrate over which the metal is deposited. This potential was found to be -100 to -60 mV for Cu2+ deposited over glassy carbon in sulphuric acid medium and -160 to -100 mV in hydrochloric acid + sodium acetate medium. A linear calibration plot for Cu2+ in the concentration range Gomathi and Prabhakara Rao - Potentiometric stripping method for estimating copper € 1  V Fig.2. Potentiometric stripping curve for copper deposited from 10-4M CuSO, in 0.1N CHJCOONa + 0.1N HCl (pH 2.87) Preconcentra- tion - 5 mins Fig.3. Linear calibration plot of stripping time versus cncentration of :opper in the concentration range 10-sM to 10-4M; Background - 0.5M Y2S04 Preconcentration - 5 mins 1 t 4 M  to 10-W vs stripping time, i s  0.5 M sulphuric acid medium is  represented in Fig.3. The above procedure was then applied for the estima- tion of copper in synthetic samples of waste streams from common metal plating industries, taking a typical composition for the effluent C I] . It is noted that the stripping time for copper deposited from the effluent in the concentration range Ith to 10-4M was comparable to the stripping time from pure sample solutions when other metal ions like Cd, Pb. Sn are present in their lower limits. The potentiometric stripping curve for copper deposited from the effluent containing one tenth of the upper limit of the constituents (Table I )  i s  shown in figure 4. Table-l:Composition of raw waste streams from common metals plating Metal or other constituent Copper Nickel Chromium (total) Chromium (hexavalent) Zinc Cyanide (amenable to chlorination) Flouride Cadmium Lead l ron Tin Phosphorus Total suspended solids E I V  Fig.4. Potentiometric stripping curve for copper deposited from synthetic common metals plating effluent containing one tenth of the upper limit of the constituents in Table I 588 Bulletin of Electrochemistry 2(6) Nov-Dec 1986 Gomathi and Prabhakara Rao - Potentiometric stripping method for estimating copper I this case stripping time for copper is less than that for pure sample solu- m.  This is understandable because at the potential ( -I  .OV)applied for ,econcentration, codeposition of other metals like Pb, Cd, Sn etc. also :curs and the efficiency of copper deposition is reduced. Such difficulty In be circumvented by obtaining special calibration graph, making the andards identical to that of the sample solution. A simultaneous deter- ,ination of various metal ions like Pb, Cd, Sn, Cu, etc. in the effluent possible by this procedure and attention is being paid to this aspect resently. The observed potentiometric stripping can be understood in terms of le oxidation of the metal with the agency of dissolved oxygen analogous the potentiometric stripping curves that one gets on mercury coated glassy irbon. This has been substantiated ifi the present work by carrying out cperiments with completely deaerated solutions in which no well defined otentiometric stripping signal could be recorded. CONCLUSION The results obtained showed that glassy carbon (without mercury film) could be successfully employed as an electrode material for potentiometric strip- ping analysis of CuZ+ in buffered and unbuffered solutions. REFERENCES 1. U S Environmental Protection Agency Development Document for pro- posed Existing Source Pretreatment Standards for the Electroplating Point Source Category Report EPA 440/1-78/085, Washington, D.C. (February 1978) 2. F Vydra, K Stulik and E Julakova, Electrochemical Stripping Analysis. John Wiley & Sons Inc, New York (1976) 3. D Jagner, Anal Chem, 50 (1 978) 1924 4. D Jagner, Anal Chem, 51 (1979) 342 -/ 5. D Jagner, Analyst. 107 (1982) 593 /"" mtinued from page 5 86 5. One month course on Basics of Electrochemistry (1-3Y) Apr. '87) Coordinator : Dr. V.K. Venkatesan Syllabus : The course will comprise of the 4 modules as follows: Module I : Materials Science (includes properties of metals, semiconductors, thin films, etc.) Module I1 : Electrical double layer Module IV: Electrodeposition Electrode kinetics Metal Finishing Electroanalytical chemistry Electrometallurgy Electrobiology Corrosion prevention and control. Module 111 : Electrochemical power sources Course charges : Rs. 20001- for complete course and Electrochemical instrumentation Rs. 5001- for each module 6. Condensed course on Voltammetric and polarographic techniques (6-10 Apr. '87) Coordinator : Shri V. Yegnaraman Syllabus : DC, AC, square waves and other polarographic techniques - linearsweeplcyclic, hydrodynamic and stripping voltammetric techniques - chronomethods - kinetic and analytical aspects - instrumentation. Course charges : Rs. 5001- 7. Condensed course on Ion selective electrodes (13-17 Apr. '87) Coordinator : Dr. Navin ~ h a n d r a  Syllabus : Importance of quality control - potentiometry - classification of ion selective electrodes - basic concepts - solid membrane ISE - liquid membrane ISE - gas sensors - microelec- trodes - techniques of ISE analysis. Course charges : Rs. 5001- -- - 8. Condensed course on Biofouling and marine corrosion (2054 Apr. '87) Coordinator : Dr. G. Rajagopal Syllabus : Types of corrosion - corrosion fundamentals - forms of corrosion - immersion corrosion - influence of oxygen - dissolved salts - pH - temp - velocity - corrosion in splash areas - metallurgical aspects - biofouling by algae - bacteria - barrades - marine growth - control measures - antifouling treatments - coatings for corrosion prevention in marine environments - cathodic protection systems - design and testing C-P systems - corrosion monitoring - corrosion of concrete. Course charges : Rs. 5001- For details, please contact: Director, Central Electrochemical Research Institute, Karaikudi-623 006, Tamil Nadu. Bulletin of Electrochemistry 2(6) Nov-Dec 15B6 58! 

A simple potentiometric stripping method for copper in plating waste

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