Investigation On The Purification Of Diamond Tailings Integrating With The Preparation Of Graphite Oxide And Its Adsorption Property

As the largest manufacturer of synthetic diamonds in the world,China produces more than 90%of the world's synthetic diamonds every year.Purification is an important technology step for the production of synthetic diamond.The traditional purification technique consumes a large amount of acid,discharges a lot of waste acid and acid mist,etc.Moreover,the graphite in the diamond tailings is oxidized to carbon dioxide,which not only emits the greenhouse gases but also wastes graphite resources.Therefore,it is necessary to further study the purification process of synthetic diamond.In this paper,the synthetic diamond tailings was separated into magnetic separation concentrate and magnetic separation tailings through magnetic separation method.Then,the graphite in the magnetic separation tailings was oxidized by a method similar to the Hummers method.Subsequently,the diamond and graphite oxide in the suspension solution were separated by the settling separation method.XRD,Raman,FT-IR and SEM were used to characterize the as-obtained diamond and graphite oxide.The dosage of potassium permanganate,sodium nitrate and concentrated sulfuric acid,as well as the reaction time in low temperature?under 5??,medium temperature?35??and high temperature?90??had changed respectively to explore the influence factor of diamond purity and oxidation degree of graphite oxide.Finally,the adsorption properties of graphite oxide to methylene blue dye were investigated.For the process carried out in this paper,the graphite in the diamond separation tailings was oxidized into graphite oxide.In view of the differences between the hydrophilcity and density of diamond and those of graphite oxide,settling separation method was used to separate diamond and graphite oxide.This method reduced the amount of acid utilized and the environment pollution from the waste acid dischatged.Furthermore,graphite was transformed into graphite oxide instead of CO₂,which not only eliminated the emission of greenhouse gas but also utilized the waste graphite and obtained graphite oxide simultaneously.The results show that the content of catalyst metal,graphite and diamond in diamond tailings was about 45 wt%,17 wt%and 38 wt%respectively.Through magnetic separation,most of the catalytic metal?magnetic separation concentrate?can be separated from the diamond tailings,in which the content of diamond was just2.4 wt%.The content of catalytic metal in the magnetic separation tailings was just7.4 wt%.With the enhancement of potassium permanganate dosage,the purity of as-obtained diamond changed little,but the recovery rate of diamond increased gradually to 99.54%,and the oxidation degree of graphite oxide increased step by step.With the increasing of sodium nitrate dosage,the interlayer spacing of graphite oxide increase gradually,but the purity and recovery of diamond were hardly affected.When the amount of concentrated sulfuric acid was 23 mL,no graphite or graphite oxide appeared in the as-obtained diamond samples.The disorder degree of the obtained graphite was the largest,and the recovery rate of diamond reached 99.33%.The reaction time of low temperature step had little effect on the purity of the as-obtained diamond samples,but the disorder degree of graphite oxide increased gradually with the extension of reaction time.When the reaction time in the medium temperature step was short,graphite existed in the as-obtained diamond sample and graphite oxide sample.With the increase of medium temperature reaction time,the graphite in the as-obtained diamond disappeared gradually,and the disorder degree of graphite oxide increased inch by inch.The amount of oxygen-containing functional groups decreased with the time extension at the high temperature reaction stage.The optimal purification parameters of magnetic separation tailings are determined as following,5 g of magnetic separation tailings,23 mL of concentrated sulfuric acid,6g of potassium permanganate and no addition of sodium nitrate,as well as reaction at low temperature,medium temperature and high temperature stages for 1 h,1.5 h and0.5 h respectively.Under the optimal purification parameters stated above,the high purity of diamond was obtained and the recovery rate of diamond reached 98.99%.The residue SiO₂,which was decomposed from the pyrophyllite and attached to the diamond surface,can be removed effectively by the reaction with the NaOH solution.Graphite oxide obtained from the purification process has a large adsorption capacity to methylene blue.The adsorption amount achieved high level when adsorbed for just 5 min,and then it increased gradually and reached equilibrium with the extension of adsorption time.The adsorption process met the pseudo-second-order kinetic model.With the increasing of the dosage of potassium permanganate,sodium nitrate and concentrated sulfuric acid,as well as the time prolonging of low temperature,medium temperature or high temperature reaction,respectively,the equilibrium adsorption capacity of graphite oxide increased gradually.The equilibrium adsorption capacity of the graphite oxide obtained under the optimal purification parameters reached 633 mg/g.