Removal of Cd2+ ion from diluted aqueous solutions by electrodeposition on reticulated vitreous carbon electrodes

Abstract

A eletrodeposição do íon Cd 2+ foi investigada em soluções aeradas de ácido sulfúrico-sulfato de potássio em pH 4,8. Sob condições potenciostáticas, usando eletrodos de carbono vítreo reticulado (CVR) de 30, 60 e 100 poros por polegada (ppp), uma elevada eficiência de remoção foi obtida para soluções contendo 5 e 10 mg L-1 de íon Cd 2+ , na faixa de potenciais entre-0,90 e-1,10 V. Neste intervalo, a eletrodeposição do cádmio é controlada por transporte de massa e a concentração de íon Cd +2 varia exponencialmente com o tempo, seguindo uma cinética de pseudo-primeira ordem. Para a concentração 10 mg L-1 de íon Cd 2+ e usando o eletrodo de 30 ppp, as eficiências de corrente e de remoção determinadas foram, respectivamente, 45% e 96%, após 30 minutos de eletrólise a-0,90 V, enquanto para 60 ppp foram encontrados 33% e 99%, respectivamente. A voltametria de redissolução anódica com eletrodo de gota pendente de mercúrio foi empregada para monitorar a concentração do íon Cd 2+ após cada experimento de eletrodeposição. The electrodeposition of Cd 2+ ion was investigated in pH 4.8 sulfuric-sulfate solutions in the presence of dissolved O 2. In potentiostatic conditions, using reticulated vitreous carbon (RVC) electrodes of 30, 60 and 100 pores per inch (ppi), high removal efficiency values were achieved in the potential range from-0.90 to-1.10 V for solutions containing 5 and 10 mg L-1 of Cd 2+ ion. In this potential range, Cd electrodeposition is a mass transport controlled reaction and the concentration of the metallic ion decays exponentially with time following a pseudo-first order kinetics. For the 30 ppi RVC, the current efficiency and removal efficiency values found were, respectively, 45 % and 96 % for a solution containing 10 mg L-1 of Cd 2+ ion after 30 minutes electrolysis at-0.90 V while 33 % and 99% were found for the 60 ppi RVC. The concentration decay of Cd 2+ ion in the solution was monitored after each experiment by anodic stripping voltammetry at a hanging mercury drop electrode.

Removal of Pb(II) from simulated wastewaters using a stainless-steel wool cathode in a flow-through cell

“…When 250 lA cm )2 was applied to the electrode, an exponential concentration decay was not observed, but it was for 400 lA cm )2 . Other authors have usually found exponential concentration decay under mass transfer conditions [6,7,[10][11][12][13]. The total charges (in coulombs) involved in each electrolysis are indicated in parenthesis.…”

“…After a 30-min electrolysis at the flow rate of 250 l h )1 , 65% removal was achieved at )0.80 V and 81% at )0.90 V. The current efficiencies were less than 20% (see Table 3) due to hydrogen evolution, oxygen and nitrate reduction, which take place simultaneously with the Pb(II) reduction and consume most of the charge. Other authors investigated the removal of different metals using RVC cathodes in aerated solutions and also found low values for the current efficiency [6,10,11,13]. It is important to point out that the reduction of dissolved O 2 must be the predominant process that contributes for the low values of current efficiency.…”

“…Three-dimensional porous cathodes, as well as the materials used for this purpose, have been extensively studied throughout the years [5][6][7][8][9][10][11]. The percolation of the electrolyte through these cathodes allows the achievement of both large electrode surface areas and high mass transfer rates for the electrochemical reactions.…”

Electrolytic magnesium recovery from drinking water membrane residuals

“…Efficient and economical electrochemical processes have been used in industry for decades for applications such as electroplating and chlor-alkali synthesis [11]. Of late, electrochemistry has been employed as a technique to treat various waste streams [12][13][14][15][16][17][18]. Metals such as copper, nickel and cadmium have been readily electrodeposited from various aqueous waste streams [12][13][14][15][16][17].…”

“…Of late, electrochemistry has been employed as a technique to treat various waste streams [12][13][14][15][16][17][18]. Metals such as copper, nickel and cadmium have been readily electrodeposited from various aqueous waste streams [12][13][14][15][16][17]. Cathodic reduction and decolorization of nanofiltration concentrate containing azo dyes from textile and printing waste has also been tested [19], with a color reduction of 60-80% being reported.…”