The N235–TOP–sulfonated kerosene system was applied for the recovery of Ge(IV) from a synthetic sulfuric acid leaching solution of secondary zinc oxide , containing Ge(IV), Zn(II), As(III), Fe(III), Si(IV), and Cd(II). The co-extraction of As(III) with Ge(IV) is a challenging problem in the extraction of Ge(IV) from aqueous solution by N235. However, TOP, as a modifier, suppressed the co-extraction of As(III) significantly. The effects of factors including N235 concentration, extraction time, tartaric acid to Ge(IV) molar ratio and temperature on the extractions of Ge(IV) and As(III) were studied. At an organic/aqueous (O/A) phase ratio of 1/1, aqueous phase pH of 1.2, extraction time of 10.5 min, tartaric acid-to-Ge(IV) molar ratio of 5.0, and temperature of 25 °C, the extraction efficiency of Ge(IV) reached 93.9%, whereas only 1.3% of As(III) was extracted by the 25%(v/v)N235–10%(v/v) TOP–sulfonated kerosene system in a single stage extraction. The Ge(IV) in the raffinate was less than 1.5 mg/L when employing a five-stage continuous countercurrent extraction at an O/A ratio of 1/10. In addition, aqueous NaOH solution of 0.5 mol/L was an appropriate reagent for the stripping of both Ge(IV) and As(III) at an O/A ratio of 1/1 and 25 °C for 10.0 min.
Hongrui Xiang,Feiping Zhao,Tao Wu,Xiaowei Zhang,Fei Chai,Qingwei Wang,Eveliina Repo,Xiaobo Min,Zhang Lin
Understanding the structure–activity relationship between the adsorption performance and accessible adsorption sites plays a vital role in developing efficient adsorbents for Ge(IV) recovery. Herein, three chitosan-based adsorbents were designed by grafting chitosan with p -hydroxybenzoic acid (HBA-CS), 3,4-dihydroxybenzoic acid (DBA-CS), and 3,4,5-trihydroxybenzoic acid (TBA-CS), and the phenolic hydroxyl amounts induced steric effect on Ge(IV) recovery was investigated. The results show that phenolic acids were successfully grafted onto the chitosan surface by an amidation reaction. The adsorption behavior of DBA-CS and TBA-CS conforms to the pseudo-second-order kinetic and Langmuir isotherm models, indicating that it is a single layer adsorption and chemisorption is the main adsorption process . The Ge(IV) recovery performance is correlated with the arrangement of the active adsorption sites and follows the order of TBA-CS > DBA-CS > HBA-CS. The steric effect of TBA-CS is more ideal than that of DBA-CS due to more phenolic hydroxyl groups, which endows it better affinity toward Ge(IV). Additionally, TBA-CS exhibits superior selectivity in the presence of competitive cations and interfering anions, and the adsorption efficiency was not significantly decreased after four regeneration cycles by the acid elution. The chelation adsorption sites for Ge(IV) provided by the o -phenolic hydroxyl groups are the dominant contribution, and the hydrogen bond and ideal steric effect further enhance the adsorption performance of TBA-CS. The structure regulation designed by steric hindrance optimization strategy to achieve high affinity is an attractive approach, which could be extended in the recovery of precious metal ions.
In this work, chitosan was modified by extracting the polyphenols rich in pomegranate peels to prepare the bio-composite material (PPPs-CS), which was applied to capture the dispersed metal germanium (Ge(IV)) in wastewater. The experimental results indicate that PPPs-CS exhibits the best adsorption performance for Ge(IV) at pH 7.0 with a dosage of 0.7 g/L. The adsorption behavior conforms to the pseudo-second-order kinetics and the Langmuir model, with the maximum adsorption capacity fitted by the Langmuir model reaching 71.34 mg/g. The results of dynamic adsorption mass transfer simulations showed that the capture behavior of PPPs-CS on Ge(IV) was dominated by the chemical adsorption of monomolecular layer. The adsorption partition coefficient of PPPs-CS for Ge(IV) with coexisting metal ions of Mn(II), Cd(II), Ca(II) and Ga(III) was as high as 11.23 L/g, exhibiting a selectivity coefficient more than 3.5 times higher than that of competing ions and demonstrating superior selectivity. After five adsorption-desorption cycles, the capture rate was still greater than 87 %. DFT calculations indicated that the uptake of Ge(IV) by PPPs-CS might be due to the ion exchange and complexation between the catechol groups on the surface of the PPPs-CS and Ge(OH) 4 . The pomegranate peel polyphenols could effectively improve the diversity and chemistry of the active sites for Ge(IV) binding by chitosan and enhance the specific recognition performance for Ge(IV). Overall, PPPs-CS has significant advantages and potential as environmentally friendly and cost-effective materials for the recovery of Ge(IV) from wastewater.
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