Stabilization Of Carbon Dioxide With Chromium Slag And The Leaching Of Hexavalent Chromium

The greenhouse effect has been a hot topic and carbon emission reduction has caused the attention of governments.Carbon dioxide emissions not only hamper the economic development,but also trouble human lives.In order to mitigate the green house effect,carbon dioxide capture and storage?CCS?is of rapid development and mineral storage is of high expectation.Because of mining and preparing ore,the cost of mineral carbonation using the ore is expensive.Alkaline industrial wastes are the most suitable replacement due to the wide source and low cost.As one of the alkaline industrial wastes,chromium slag affects the surrounding environment and harms people's lives.The hexavalent chromium is significantly harmful because of its carcinogenicity,high solubility and faster mobility.This paper combines the treatment of chromium slag with carbon emission reduction,and takes advantage of their unique properties to treat them simultaneously.Firstly,the setup for mineral carbonation was used.The factors of temperature,water to solid ratio?W/S?,reaction pressure and time were investigated in the process of the storage of CO₂ with chromium slag.The amount of CO₂ storage and the end-product of carbonation in the slag were analyzed by powder X-ray diffraction and thermal analysis.Then,a dynamic leaching experiment of chromium slag was designed to testify the ability of CO₂ adsorption onto chromium slag and to release Cr???for stabilization.In the process of CO₂ storage by chromium slag,the optimum reaction conditions were the temperature of 120?,the pressure of 1 MPa,the W/S of 0.2 and the reaction time of 2h.At aforementioned condition,CaCO3 and MgCO3·3H2O are end-products of CO₂ storage in the slag,in which the carbonation degree of CaO and MgO were 38.3%and 1.1%,respectively.Finally,the amount of CO₂ storage by chromium-slag is 102.6 g/kg.The leaching of Cr???in chromium slag showed that the addition of carbon dioxide can promote the release of Cr???from the chromium slag and reduce the pH of the washing solution.Further research indicated that the higher concentration of CO₂ and the smaller particle size of slag are beneficial to the CO₂ storage and the leaching of Cr???.Finally,ca.89 mg/g CO₂ was adsorbed and ca.2.6 mg/g Cr???was released from the chromium slag?<380?m?using pure CO₂ in the experiment.Calcite is the only carbonate species and the extent of carbonation is 18.46%in the post-carbonated slag.Thus,the combine of CO₂ and chromium slag can realize waste control by waste.Chromium-slag can be used for CO₂ storage by mineral carbonation.In addition,as washing solution,CO₂ can promote the release of Cr?VI?from chromium-slag,and the sequestration of the CO₂ is realized simultaneously at ordinary temperature and pressure.