Preparation Of Poly (M-Phenylenediamine) Based Materials And Study Of Their Performance In Recovering Au(Ⅲ)

With the rapid development of the world economy,human beings have produced a large amount of e-waste in the past two decades,which not only endangers the environment and groundwater,but also causes a large amount of wasted metal resources.It is estimated that about59 million tons of e-waste were generated in 2019 alone.However,only 20%of this e-waste was recycled and the remaining became the main pollutant in landfills.In the context of circular economy,the recovery of precious metals from e-waste is gaining attention,and circular economy is expected to transform e-waste into wealth.In addition,precious metals play an important role in jewelry,investment and industrial applications.Secondary sources（e.g,e-waste）are reported to contain much higher levels of precious metals than natural ores.Relative to other minerals,e-waste contains large amounts of precious metals and such waste can be considered as a secondary source of precious metals.Therefore,the recovery of gold from e-waste is of great importance for the economy and the environment.In order to solve this problem,this project is devoted to the synthesis of adsorbents with high adsorption rate and low cost using simple preparation methods,and the physical properties,chemical properties,adsorption rate and adsorption mechanism of adsorbent materials under different conditions have been studied in detail.The research work carried out at the master’s level was mainly as follows:Research work Ⅰ:In order to rapidly recover precious metal-gold from acidic solutions,we prepared a PmPD solid sphere using a one-step oxidation method and applied it to recover Au（Ⅲ）from acidic solutions.The experimental results showed that the prepared PmPD has high selectivity and treatment capacity for Au（Ⅲ）and can selectively reduce Au（Ⅲ）from a mixture of various metal ions(Cu²⁺,Ni²⁺,Cd²⁺,Zn²⁺,Au（Ⅲ）),and the maximum treatment capacity of PmPD for Au（Ⅲ）under the solution p H of 3.0 reached in 4 h Ⅰn addition,the performance of PmPD was stable after several cycles of use.In addition,the treatment effect of PmPD was also advantageous in the actual CPU leachate experiments.These experimental results indicate that PmPD has a broad application prospect in recovering gold from acidic solutions.Research work Ⅱ:Based on research work Ⅰ,in order to increase the specific surface area of PmPD,in this research work,we prepared a new hollow PmPD by sacrificial template method and applied it to the rapid and selective recovery of Au（Ⅲ）from aqueous solution.The adsorbent material can adsorb gold ions from low concentration（10 mg/L）gold solutions extremely fast（10 min）and has excellent selectivity for gold in complex metal ion mixtures containing different competing concentrations.The maximum capacity of the hollow PmPD for Au（Ⅲ）reached 1185.18 mg/g in 10 min of equilibration time at room temperature and solution p H 4.0.In addition,the hollow PmPD showed outstanding performance for multiple recycling of Au（Ⅲ）solutions.These experimental results indicate that the hollow PmPD has a promising application in recovering trace amounts of gold from strongly acidic solutions.Research work Ⅲ:In Research Work Ⅱ,PmPD nanoparticles are easy to be agglomerated in water,with reduced adsorption capacity and difficult to be separated from aqueous solution,and are easily depleted in the recycling process.In order to improve the recovery efficiency and operability of nanomaterials,we successfully prepared a soft and easy solid-liquid separation film adsorbent by cross-linking PmPD on chitosan as a substrate,which can selectively recover gold from the leachate of e-waste.The experimental results show that CS-PmPD membrane can selectively reduce Au（Ⅲ）from a mixture of metal ions(Cu²⁺,Ni²⁺,Cd²⁺,Zn²⁺,Au（Ⅲ）).When the solution p H value was 3,the maximum capacity of CS-PmPD membrane for Au（Ⅲ）reached410 mg/g within 2 h.CS-PmPD membrane can be regenerated after rinsing with sodium bisulfite solution,and its performance remains stable after seven cycles of use.In addition,the CS-PmPD membrane has obtained satisfactory results in the treatment of actual CPU gold-containing leaching solution.Research workⅣ:Based on the research work Ⅲ,in order to further improve the strength of the membrane,we used a non-solvent induced phase separation method to synthesize a new film material（PES-PmPD）with polyethersulfone and poly（m-phenylenediamine）for easy separation and applied it to selective recovery of Au（Ⅲ）from e-waste solution.The optimum conditions,adsorption capacity and selectivity of PES-PmPD membranes were investigated by adsorption experiments.The maximum adsorption capacity of PES-PmPD membranes for Au（Ⅲ）in 4 h was 582.75 mg/g at 30 ^oC and the optimum p H was 1.The adsorption process follows a pseudo-second-order adsorption isotherm.The adsorbent was characterized by XPS and XRD to understand the recovery mechanism of PES-PmPD membrane for Au（Ⅲ）.In addition,PES-PmPD membranes have a single selectivity for Au（Ⅲ）in various natural water bodies and strong acidic conditions.Therefore,the membrane material has great potential for recycling Au（Ⅲ）in discarded e-waste.