La eliminación de metales tóxicos presentes en efluentes líquidos mediante resinas de cambio iónico. Parte XIII: Zinc(II)/H+/Lewatit OC-1026

Francisco José Alguacil

doi:10.3989/revmetalm.172

Abstract

La resina de intercambio catiónico Lewatit OC-1026 (que tiene como grupo activo al acido di-2-etilhexil fosfórico adsorbido) se ha utilizado para la eliminación de zinc(II) de disoluciones acuosas. Esta eliminación se ha investigado bajo diferentes condiciones experimentales: velocidad de agitación (400-1200 min−1), temperatura (20-60 °C), pH del medio acuoso (1-4) y concentración de la resina (0,05-0,4 g·L−1). La carga de zinc(II) en la resina disminuye con el aumento de la temperatura (reacción exotérmica) en un proceso espontaneo, alcanzándose el equilibrio en tiempos mas cortos al aumentar esta variable. A 20 °C, los datos experimentales se ajustan a la cinética de pseudo-segundo orden, mientras que a 60 °C el modelo cinético que mejor representa la carga del metal en la resina es el de segundo orden. El proceso de cambio iónico depende del valor de pH del medio acuoso, disminuyendo el tanto por ciento de la carga del metal en la resina con la disminución de este valor (de 4 a 1); a pH 4, la carga del metal responde al modelo de difusión en la partícula y a la isoterma tipo-2 de Langmuir. La resina Lewatit OC-1026 presenta mejores características, respecto a la eliminación de zinc(II), que los nanotubos de carbono funcionarizados (grupos carboxílicos) y sin funcionalizar. El zinc(II) cargado en la resina puede ser eluido mediante el uso de disoluciones ácidas.

Highlights

Zinc is an essential element for life, though and excess in zinc exposure is detrimental for human health because it causes nausea, diarrhea, headaches and losses of essential copper and iron in human body (Chasapis et al, 2012; Maret, 2013).There are not stringent regulations about maximum zinc allowance in drinking water, though from a zinc concentration above 3 mg·L−1, water tends to be opalescent, develops a greasy film when boiled, and has an undesirable astringent taste (WHO, 2020)
Several procedures aimed to the removal of this element from aqueous solutions had been already reported (Abdelrahman et al, 2019; Aliyu, 2019; Gümüş, 2019; Sakalova et al, 2019; Mirjavadi et al, 2019; Zand and Abyaneh, 2019; Ahmad et al, 2020; Wieszczycka et al, 2020; Zhang et al, 2020), all of them are based in the adsorption of Zn2+onto different adsorbents
A distinctive difference of this resin with others used in these series of works, is that in the present case, Lewatit OC-1026 has a liquid-liquid extraction reagent adsorbed in the resin matrix as functional group, which in the present case (Fig. 1) is an organic phosphorous derivative (D2EHPA), in the case of zinc(II), metal uptake onto the resin is represented by the equilibrium: 2((RO)2 PO(OH))r + Zna2q+ ⇔

Summary

INTRODUCTION

Zinc is an essential element for life, though and excess in zinc exposure (ingesta) is detrimental for human health because it causes nausea, diarrhea, headaches and losses of essential copper and iron in human body (Chasapis et al, 2012; Maret, 2013). In the USA, there was not a general rule about zinc allowances in waters, i.e. i) if the effluent comes from an electroplating facility, the daily limit for zinc is 0.6 mg·L−1, ii) if the facility is engaged in chemical etching and milling, the daily limit is 164 mg·L−1, and iii) in the steam electric power generating industry, the daily limit is 1.0 mg·L−1 These differences are a function of the ability of the specific industry to treat its wastewater and remove the pollutants using technology applicable to that industry at the time that USEPA studied the industry (Walker Jr., 2020). The elution of zinc(II) from metal-loaded resin by acidic solutions is described

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS