Electrochemical recovery of zinc from the spent pickling baths coming from the hot dip galvanizing industry. Potentiostatic operation

Abstract

ElsevierCarrillo Abad, J.; García Gabaldón, M.; Ortega Navarro, EM.; Pérez-Herranz, V. (2011). Electrochemical recovery of zinc from the spent pickling baths coming from the hot dip galvanizing industry. Potentiostatic operation. Separation and Purification Technology. 81 (2) Keywords: electrochemical deposition, iron, hydrogen evolution reaction, pickling solutions, zinc electrodeposition AbstractAn electrochemical reactor was developed to recover zinc from the spent pickling solutions coming from the hot dip galvanizing industry. These solutions mainly contain ZnCl 2 and FeCl 2 in aqueous HCl media. The effect of the applied potential on the figures of merit (fractional conversion, current efficiency, space-time yield and specific energy consumption) of the electrochemical reactor was analysed. Voltammetric experiments were performed previously in order to select the optimum conditions to be applied in the electrolysis experiments. From the i-V curves it was inferred that bulk zinc deposition started from potential values more cathodic than -0.99V. The hydrogen evolution reaction (HER) appeared from -0.45V and masked the zinc cathodic peak C1, 2 related to bulk zinc deposition, at high HCl concentrations. The presence of HCl inhibited iron deposition in synthetic samples. The additives present in the real baths, which diminish the massive hydrogen generation, allowed the observation of peak C1.The potential values to be applied in the electrolysis experiments were chosen from the voltammetric experiments and ranged between -1V and -1.75V. In the absence of iron in solution, as the electrode potential was shifted towards more negative values, the space-time yield of zinc and its fractional conversion increased because of the increase in the electrode roughness and the hydrogen turbulence-promoting action.Simultaneously, the specific energy consumption decreased initially due to the increase in the zinc conversion rate but decreased for the most cathodic potential value due to HER. The presence of iron in synthetic solutions led to a decrease in current efficiency associated with the reverse redox Fe 2+ /Fe 3+ system and to the enhancement of the HER, which also induced increments in the local pH and the subsequent zinc redissolution for the most cathodic potential values. On the contrary, the additives present in the real spent pickling baths avoided the adverse effects of iron, and zinc electrodeposition was possible even at high cathodic potential values. In fact, a potential value of -1.75V was selected as the optimum since the conversion, the current efficiency and the space time yield obtained in the real baths were relatively high.3

Treatment of spent pickling baths coming from hot dip galvanizing by means of an electrochemical membrane reactor

“…6. For both cases, η increases with the applied current because of the turbulence promoting action of hydrogen evolution, the increase of the electrode surface roughness and the higher velocity of the electrochemical reactions [9]. On the other hand, comparing the results obtained for both reactors, OCR experiments initially presents higher η due to the lower reactor volume.…”

“…The one cell reactor (OCR) and the membrane reactor used in this work were well defined in our previous works [9,13]. However, a scheme of the two reactors employed in this work together with the main reactions taking place on both electrodes is presented in Fig.…”

“…This sampling volume has been taken into account and all the figures of merit have been recalculated. Zinc and iron determination was performed by atomic absorption spectrophotometry (AAS) as described in our previous works [9,10,13]. The determination of zinc is performed on a Perkin-Elmer model Analyst 100…”

“…In a previous work [8], the authors carried out an electrochemical study of the spent bath to obtain the electrochemical processes kinetics. Subsequently, a one cell electrochemical batch reactor was used in potentiostatic and galvanostatic mode [9,10] in order to determine the viability of zinc recovery. During these experiments, zinc redissolution was observed at long time values for all the experimental conditions.…”

Recovery of zinc from spent pickling solutions using an electrochemical reactor in presence and absence of an anion-exchange membrane: Galvanostatic operation

“…Moreover, the electrolytic recovery of zinc present in the spent pickling baths is a suitable technique because zinc electrowinning has been practiced for many years [6]. In fact, 80% of world zinc production is obtained by electrowinning [1].In our previous paper [7], the potentiostatic recovery of zinc present in the spent pickling bath using an electrochemical reactor was studied. The major interfering reaction during zinc electrodeposition on the cathode surface was the hydrogen evolution reaction (HER), although iron presence also diminished the current efficiency.…”