Tratamento de licor sulfúrico rico em níquel visando á remoção de cobalto

Abstract

The cobalt extraction from a synthetic nickel-rich liquor, containing approximately 50g/L of nickel, 5.0g/L of cobalt and 11.3g/L sodium, using the liquid surfactant membrane technique (LSM), was evaluated in this study. A técnica MLS consiste de uma emulsão primária, constituída pelo solvente contendo um surfatante e uma solução de reextração, dispersa em fase alimentação (licor), formando uma emulsão múltipla. The LSM technique consists of an primary emulsion, constituted of the solvent phase containing a surfactant and the stripping solution, dispersed in the feed (liquor) phase, forming a multiple emulsion. Due to the position which each phase appears in the system, they are called the inner phase (IP), the membrane phase (MP) and the external phase (EP). This technique has a high extraction capacity coupled with a high selectivity. Thus, the aim of this study was the depletion of cobalt in order to purify a nickel-rich liquor with a minimum possible nickel extraction. There are several variables that affect the extraction and selectivity of the process, some of which were investigated in this work. The best results were obtained with the following operating conditions: pH of the feed phase = 4.5, concentration of the extractant Cyanex® 272 = 1.2v/v (1.1% w/v), permeation time = 40 min, concentration of the surfactant ECA 4360 in MP = 2.0%v/v, [H2SO4] in IP = 1.5mol/L and T = 40°C. The multistage extraction system was investigated, firstly, evaluating the depletion of cobalt from the external phase, with a cross-current contact of fresh primary emulsion and liquor. In terms of total or cumulative extraction, after four stages, the system reached 98% of extraction and with five stages practically all cobalt present in the liquor was extracted (99.6%). Further, the ability to extract of the reused membrane phase was evaluated, with a cross-current contact of a new liquor and primary emulsion prepared from the membrane phase after the demulsification and reemulsified with a virgin internal phase. Three stages were investigated, with no loss in the extraction capacity of the membrane phase. Finally, the liquor and the primary emulsion were put together by a co-current contact and the depletion of the liquor occurred in conjunction with the reuse of the membrane phase. In this system, a total of 90% of cobalt extraction was obtained in three investigated stages of a system which simulated a continuous operation in mixers-settlers. Comparing the results of this study with the results shown in the Cytec’s catalog for solvent extraction, even for different liquors, it is observed that the amount of extractant used in the LSM system is, in this case, about 3% of that used in solvent extraction.