The Thermal Decomposition Of Phosphogypsum Assisted With H₂S And The Mineralization Of CO₂ With The Residue In Three-phase Fluidized Bed

Produced during the production of wet-process phosphoric acid,phosphogypsum is a massive waste cotaining over 90%CaSO₄·2H₂O.At present the global producees about 2800 million tons per year with China contributing 70 million of them.Phosphogypsum,for its large amount of emission,low rate of ultilization and great harm to the environment,has become a serious source of solid pollution,undermining the development of phorphorous chemical industry.In addition,stacking of phosphogypsum has also resulted in environement pollution and huge waste of land,manpower,material resource and financial resource.Faced with multiple pressure,its ultilization has become a hotspot in the field,pivital to the sustainable development of phorphorous chemical industry.One way to realize the effective ultilization of phosphogypsum is by processing the waste into widely-used material carbonate calcium,which is still in study stage.As a consequence of the huge energy consumption world wide,tons of carbon dioxide have been released into the atmosphere,causing melting iceberg,rising sea level,degenerating ecosystem and frequent natural desasters,thus putting regionl inhabitants at great risk.Containing the rising level of CO₂ in the air is key to environment protection.The viable approaches for carbon dioxide capture includes marine sequestration,floristic carbon fixation and landfill.Studies found that carbon in carbonates rather than in carbon dioxide is the most stable form.Therefore,researchers started turning to carbon dioxide capture and storage in the form of carbonates?mainly calcium carbonate and magnesium carbonate?,the key to which is the ions--Ca²⁺ and Mg²⁺.Aiming to solving some problems in disposal and utilization of phosphogypsum and carbon dioxide,the author conducted series of experiments where the calcium in phosphogypsum was first thermally decomposed into calcium sulfide in the residue and then used to capture carbon dioxide;the analysis on the mechanism and the effects of several factors,along with the process of mineralization were stated in the paper.Hopefully this work will be of value to designing a feasible process route for producing carbonate calcium with phosphogypsum and carbon dioxide,reaching the goal of "waste control by waste and full recycle of the waste".The main research contents include:?1?Simulations on reaction systems of phosphogypsum with hydrogen sulfide,phosphogypsum with hydrogen sulfide and carbon monoxide were performed using Equilibrium and Reaction modules of FactSage 7.0.The calculation results showed that phosphogypsum's decomposition into calcium sulfide in reductive atmosphere follows gas-solid reaction mechanism;and that where the decomposition of phosphogypsum takes place at 800? with hydrogen sulfide,?2?The author investigated the effects factors including reaction temperature,reaction time,addictive,proportion of the two reductants have on the phosphogypsum's decomposition into calcium sulfide through a tubular furnance.The results revealed that all the factors mentioned above had an influence on the reaction.In particular,at 45min,950? and with calcium chloride or iron oxide added,a decomposition rate of 95%above and residues containing over 80 wt.%CaS were obtained,whereas adding magnesium oxide under the same condition had little effect on the rates of decomposition and yield.In the case of dual reductant atmosphere,it's worth notice that when the proportion of the two reductants was 1:1,a decomposition rate of over 95%and a calcium sulfide content of more than 85%in the residues were obtained.The experiments also suggested an advantage of using mixed gas of CO and H₂S over either one of them.?3?The author also investigated the effects of reaction temperature,reaction time,liquid-solid ratio,flow of carbon dioxide on carbonate calcium's production from the mineralization of CO₂ in a three-phase fluidized bed.A conversion of over 97%for calcium sulfide to carbonate calcium was observed at 45 min,25?,liquid-solid ratio of 8 mL/g and CO₂ flow of 300 mL/min.?4?According to the thermodynamic simulation results of the reaction system of calcium in phosphogypsum and carbon dioxide,the mineralization of CO₂ follows two mechanisms--gas-liquid and liquid-solid reactions.The mineralization occurs in liquid phase.