Electrochemical determination of thiourea and glue in the industrial copper electrolyte
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I. INTRODUCTION
IN the industrial copper electrorefining process from acidified copper sulfate solutions, organic substances such as collagen (glue) and thiourea added in small amount to the electrolyte are very important. The presence of these reagents affects the mechanism of the electrolytic reduction process ~ and the structure of the cathode deposit. The concentrations of these substances decrease during the process as a result of co-deposition (mainly thiourea) and hydrolysis (glue). Therefore it is necessary to add them to the electrolyte in a continuous way. However, a too-high concentration of smoothing reagents has an equally detrimental effect on the structure of cathodes as their absence. In order to obtain a pure and smooth cathode deposit, a constant concentration of active substances in the electrolyte should be maintained. A quantitative determination of these substances is, therefore, very important. The azide method proposed by Kurzawa z is suitable for determination of thiourea in excess copper(II) ions but is not applicable to industrial electrolyte. This electrolyte contains variable amounts of Fe(lI), As(Ill), and Sb(III) ions. It was found3 that in the test electrolyte containing As(III) and/or Sb(III) the amount of thiourea determined by Kurzawa's method is larger than that added to this solution. It is caused by the fact that in this method thiourea is determined indirectly, and the reactions which occur in this system are very complex. Because sodium arsenite is used for the titration, As(Ill) especially interferes in the thiourea determination. The surface active substances influence the polarization potential of the cathode. The potential dependence on glue concentration was used by Andersen et al. 4 for the determination of glue amount in industrial electrolyte. The method suggested in the present paper enables simultaneous determination of the concentrations of the two most important leveling reagents, i.e., of glue and thiourea. II.
EXPERIMENTAL
A. Apparatus and Reagents
Measurements were carried out on an LP-60 polarograph and Radelkis OH-105 polarograph. A copper disc diameter S. KRZEWSKA and H. PODSIADLY, Lecturers, L. PAJDOWSKI, Professor, and J. PODSIADLY, Assistant, are all with the Institute of Chemistry, Wrcw./aw University, E Joliot-Curie 14, 50 383 Wroc/'aw, Poland. Manuscript submitted October 12, 1981. METALLURGICALTRANSACTIONSB
0.03 cm was used as a microcathode. A cylinder made of refined copper foil of 80 cm 2 surface area served as an anode. The anode potential was independent of the current and its value measured vs Hg, Hg2SO4, K2SO4 sat. was 385 inV. The copper microcathode polarization potential value was measured vs the anode. The standard electrolyte consisted of 45 g/1 Cu 2+ as CuSO4, and 160 g/l H2SO4. An industrial electrolyte from Copper Electrorefinery-Legnica was used, as well as the gelatin ("Fototechnika" Wroclaw Technical University) of molecular weight 100030 and the bone glue "Pollena" Dabrowa G6rn. d--- 1.9 IIs. (PN72/8182-02). Other reagents were
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