Analysis Of Pyrolysis Characteristics Of Electrolytic Manganese Slag And Its Application In Ceramsite Proppant

Electrolytic manganese residue（EMR）,a by-product of the electrolytic metal manganese process,is produced by the acid leaching,neutralization and filter press treatment of the manganese carbonate powder.And the amount of accumulated EMR in the past several decades was more than 120 million tons and is increasing at a rate of 10 million tons per year.How to safely handle and effectively use them is an important issue facing the development of the industry.The comprehensive utilization rate of electrolytic manganese slag is low,and its disposal methods are mainly stacked and landfilled.This not only causes a waste of resources,but also poses a greater environmental safety hazard.Ceramsite proppant is a filling material used for oil and gas exploitation using hydraulic fracturing technology.The ceramsite proppant is mainly prepared with high-grade bauxite as the raw material through granulation and high-temperature calcination.The electrolytic manganese slag contains a lot of silicon and calcium components,which can be used as auxiliary materials and bauxite to study the preparation of low-density ceramsite proppants.A small amount of Fe₂O₃,MgO,MnO and other metal oxides in the composition of electrolytic manganese slag produce a liquid phase during high-temperature sintering,which can effectively reduce the product sintering temperature,promote the sintering and densification of materials,and improve the mechanical strength.Therefore,the electrolytic manganese slag is used as an auxiliary raw material for ceramsite proppant to research.In this background,this article uses bauxite from Guizhou Xinyineng Propant Company as the main raw material and electrolytic manganese slag from Southwest Manganese Mine Co.,Ltd.as auxiliary materials to prepare low density ceramsite proppant through homogenization,conventional,granulation,and sintering processes,which provides theoretical support for the comprehensive utilization of electrolytic manganese slag.The main findings are as follows:（1）The analysis results of the physical and chemical properties of electrolytic manganese slag show that the loose bulk density of electrolytic manganese slag is1.00g/cm³,the close bulk density is 1.501g/cm³,and the moisture content is about23.45%.Its main chemical components are SO₃（26.64wt%）,SiO₂（20.27wt%）and CaO（11.48wt%）,containing a small amount of Al₂O₃（6.37wt%）,Fe₂O₃（2.50wt%）,MgO（2.97wt%）and Mn O（1.92wt%）.The mineral composition is mainly quartz and dihydrate gypsum,and contains a small amount of ammonium salt compounds with poor crystallinity in the form of ammonium sulfate,ammonium magnesium vanadium and other double salts.（2）The thermogravimetric method combined with Fourier transform infrared spectroscopy-mass spectrometry and kinetic model were used to study the possible reaction mechanism of the pyrolysis process of electrolytic manganese slag and the change law of pyrolysis volatiles release characteristics were analyzed.The result shows that the pyrolysis process of electrolytic manganese residue can be divided into five processes:the dehydration of CaSO₄·2H₂O,the removal of ammonium salt compounds,the transformation of anhydrous CaSO₄ crystal form,the decomposition of carbon-containing organic matter and the solid-phase reaction between the substances to form a new phase.According to the difference of activation energy values,the kinetic process for the pyrolysis of electrolytic manganese residue was divided into four sections.The pyrolysis reaction mechanism functions for different kinetic mechanism were the second-order phase boundary chemical reaction function:g（α）=（1-α）^-1,Mampel Power law function g（α）=α^1/4,2/3-order phase boundary chemical reaction function g（α）=（1-α）^-1/2 and three-dimensional diffusion function g（α）=[1-（1-α）^1/3]^1/2.The major gases released during the pyrolysis of electrolytic manganese residue were NH₃,CO₂ and SO₂.The intermediate product of CO was unstable and participated in the reaction to promote the formation of CO₂ and SO₂.（3）The pre-calcining process is used to improve the quality of the electrolytic manganese slag and reduce impurities.The results show that the removal rate of ammonia nitrogen in the electrolytic manganese slag is less than 30%after calcination at 200°C,the removal rate of ammonia nitrogen can reach about 70%after calcination at 500°C,and the removal rate of ammonia nitrogen can reach about 100%after calcination at 700°C.The main chemical components of electrolytic manganese slag clinker are:SO₃（30.68wt%）,SiO₂（29.04wt%）and CaO（15.21wt%）,and contain a small amount of Al₂O₃（11.11wt%）,Fe₂O₃（3.60wt%）,and MgO（3.92wt%）;the main phase components are quartz（SiO₂）and anhydrous gypsum（CaSO₄）.（4）The electrolytic manganese slag was used as an auxiliary material to prepare ceramsite proppant.The results show that when the the electrolytic manganese slag is used as an auxiliary material to study the preparation of ceramsite proppant.The results show that when the additionof electrolytic manganese slag increases from 0%to 15%,the bulk density of ceramsite proppant decreases from1.60g/cm³ to 1.46g/cm³,and the apparent density decreases from 3.07g/cm³ to2.87g/cm³,the broken rate of was increased from 4.33%to 10.16%under the closed closure pressure of 52MPa.This is because the calcareous raw material in the electrolytic manganese slag forms a new phase of anorthite during the high temperature process.At the same time,too much liquid phase is produced and wrapped around the corundum and mullite crystal grains,which hinders the formation of mullite phase and the development of crystal forms to a certain extent,resulting in the decrease of the strength of the ceramsite proppant.（5）The electrolytic manganese slag clinker is used as an auxiliary material to study the preparation of ceramsite proppant.The results show that the incorporation of electrolytic manganese slag clinker is 15%,and the sintering temperature is 1250°C and the sintering time is 2h.The crushing rate of the ceramsite proppant obtained material under 52MPa closing pressure is 6.67%（<10%）;The bulk density and apparent density are 1.42g/cm³,2.89g/cm³ low-density medium-strength ceramsite proppant.The phase composition of the material is cubic corundum,quartz and a small amount of anorthite phase.The pore diameter is mainly concentrated at 3.88 nm.The specific surface area and pore volume are 0.263m²/g and 0.0034cm³/g respectively.Performance of ceramsite proppant get effective improvement.（6）Improve the performance of ceramsite proppant by introducing additives.The study found that the admixture ZrO₂ reacts with SiO₂ to form ZrSiO₄（zircon）during the sintering process,which can reduce the porosity of the material and promote the densification of the ceramsite proppant material.However,the sintering temperature and bulk density will be increased;the introduction of Al₂O₃ and diatomaceous earth can make up for the lack of Al and Si sources in the raw materials,and promote the formation of mullite phases.When the Al₂O₃incorporation was 3%,the crushing rates at 52MPa and 69MPa closing pressure were 15.56%and 24.69%,respectively,and when the diatomite addition was 3%,the crushing rates at 52MPa and 69MPa closing pressure were 10.03%and 20.63%.