The Application Of Functionalized Nano-silica In The Recovery Of Silver Ions

Silver is a precious metal that has been widely used in photography industry,electrical and electronic equipment and medical products.However,silver ion can lead to serious environmental problems and a waste of resources.Therefore,it is of particular importance to develop effective methods for separating and recovering silver.In this thesis,different structure and properties of organic functional groups were grafted to the silica nanoparticles surface for selectively adsorbing silver ions from aqueous solution.The result showed that:(1)The sulfoethyl functionalized silica nanoparticle can selectively absorb silver ions from aqueous solution,the adsorption equilibrium time was 60 min and the adsorption capacity for silver ion was 21.9 mg/g at pH 6.The adsorption isotherms fitted well with the Langmuir isotherm and the adsorption kinetics followed the pseudo-second-order kinetic model,the adsorption of silver ions is a monolayer adsorption and the rate-determining step is chemical adsorption.The adsorption mechanism is ascribed to the formation of a hexatomic chelate complex between the silver ions and sulfo and amino groups.(2)The carboxymethyl-dithiocarbamate functionalized silica nanoparticle can selectively absorb silver ions from aqueous solution,the adsorption equilibrium time was 30 min and the adsorption capacity for silver ion was 54.3 mg/g at pH 6.The adsorption isotherms fitted well with the Langmuir isotherm and the adsorption kinetics followed the pseudo-second-order kinetic model,the adsorption of silver ions is a monolayer adsorption and the rate-determining step is chemical adsorption.(3)The trithiocyanuric acid functionalized silica nanoparticle can selectively absorb silver ions from aqueous solution,the adsorption equilibrium time was 30 min and the adsorption capacity for silver ion was 80.0 mg/g at pH 6.The adsorption isotherms fitted well with the Langmuir isotherm and the adsorption kinetics followed the pseudo-second-order kinetic model,there is no obvious reduction of the removal percent of silver ions after five cycles,indicating the adsorbent have good reusability.The adsorption mechanism was ascribed to the chelating binding between silver ions and sulfo groups.