Research On Recovery Of Germanium By Phenolic Hydroxyl Functionalized Adsorbents

As a promising industrial raw material and semiconductor metal,germanium is increasingly used in photovoltaic and chip industries.At present,germanium mainly prepared from the by-products of lead-zinc hydrometallurgy process,which usually co-exists with other metal cations(such as Zn²⁺,Cu²⁺,Fe³⁺,etc.)and anions（such as F^-,Cl^-,etc.）in zinc leaching solution.There are huge problems in the traditional lead-zinc smelting industry,such as serious pollution,high energy consumption,and low selective recovery efficiency.This paper proposed a phenolic hydroxyl functionalized strategy based on the excellent selectivity for Ge（IV）and ideal steric effect of polydentate ligand phenolic hydroxyl.Firstly,two functionalized adsorbents of phenolic hydroxyl coated magnetic Fe₃O₄（Fe₃O₄@PHG）and phenolic hydroxyl grafted chitosan（PHG-CS）were prepared.The physicochemical properties and morphologies of these two materials were characterized.Then,the adsorption kinetics,isotherms and other parameter experiments of Ge（IV）adsorption onto PHG-CS were investigated.The adsorption performance and mechanisms of Ge（IV）by phenolic hydroxyl modified materials were revealed,indicating the PHG-CS has potential prospect in actual applications.The main research results are as follows:（1）Fe₃O₄@PHG was prepared by dopamine self-polymerization method.The spherical Fe₃O₄ with a diameter of 8-10 nm was coated by poly-dopamine formed a nanofilm on its surface with payload of 37.1 wt.%.The optimum adsorption pH for Ge（IV）was 6 and basically reached adsorption equilibrium at 200 min with maximum adsorption capacity of25.35 mg/g.The adsorption behavior conforms to pseudo second-order kinetics and Sips isotherm model with adsorption rate constant of1.029×10^-2 g/mg min and Sips coefficient Ns of 1.86.The adsorption process conforms chemisorption heterogeneous adsorption,and there are multiple adsorption sites on surface of Fe₃O₄@PHG.（2）PHG-CS was prepared by chemical mediate method.The phenolic hydroxyl groups were successfully grafted onto chitosan with content of2.04 mmol/g.The PHG-CS exhibited loose aerogel structure and the water contact angle decreased with the increase of the phenolic hydroxyl ligands from 82.9°to 18.8°.The optimum adsorption pH for Ge（IV）is 3 with maximum adsorption capacity of 28.34 mg/g and the adsorption behavior conforms to the pseudo second-order kinetic and Langmuir isotherm model,where the adsorption rate constant is 1.525×10^-2 g/mg min,and the distribution coefficient K_L is 0.2 L/mg,indicating that the adsorption process conforms chemisorption monolayer and homogeneous adsorption.（3）The adsorption performance of PHG-CS for Ge（IV）in aqueous solution was studied in the presence of competitive metal cations and competitive anions.The results showed that the separation constants Sel_Ge/Zn,Sel_Ge/Cu and Sel_Ge/Fe of PHG-CS are 2.37,1.38 and 0.61,respectively,showing its outstanding separation effect on Zn（II）and Cu（II）.The adsorption efficiency of PHG-CS for Ge（IV）is more than 60%when the concentration of F^-,Cl^-,SO₄^2-is less than 1 m M.The steric effect of PHG-CS with poly-ligand phenolic hydroxyl group is more ideal compared with that of mono-ligand,and the adsorption of Ge（IV）was realized by bidentate hexagon chelation.Based on this characteristic,the adsorption performance of Ge（IV）can be enhanced by phenolic hydroxyl modification for other substrate materials in future studies.（4）The recovery of germanium in zinc leaching solution by PHG-CS was studied.The results showed that the adsorption efficiency of Zn（II）,Cu（II）,Fe（III）and Ge（IV）by PHG-CS are 4.6%,6.2%,20.7%and 63.5%,respectively at pH～2,dosage of 15 g/L and adsorption time of 8 h.PHG-CS performed well for Ge（IV）adsorption in zinc leaching solution with high acidity,high concentration of multi-metals,showing its application potential in the recovery of Ge（IV）in actual zinc leaching solution.