Foundmental Study On Preparation Of Cementious Materials By Water-washed Electrolytic Manganese Residue

Electrolytic manganese residue（EMR）is an acid waste residue produced by the production of electrolytic metallic manganese（EMM）.With the rapid development of the EMM industry,EMR has become a bottleneck restricting the development of the EMM industry.Preparing cement-based materials with EMR is an important way to realize its recycling,since it could reduce the production cost of cement-based materials,reduce CO₂emissions,and help achieving the goal of“double carbon”.However,due to the high content of NH₄⁺,SO₄^2-and heavy metals such as Mn²⁺,and low activity,EMR is not widely used in cement-based materials.To recover Mn²⁺from EMR and remove soluble NH₄⁺,SO₄^2-and Mn²⁺,some enterprises adopt multi-stage counterflow washing and pressed filtration process.During this process,there are still some NH₄⁺,SO₄^2-and Mn²⁺remaining in the water-washed EMR（WEMR）cake,which still affect the product quality when used as cement-based materials,and this method does not improve the activity of WEMR.Therefore,EMR pretreated by carbide slag（CS）were systematically studied for its process and mechanism,and NH₄⁺removal from WEMR as well as heavy metals such as Mn²⁺solidification was realized.The pozzolanic activity of the deaminated WEMR（DWEMR）was improved by mechanical-thermal activation.The basic properties,micro-properties and hydration mechanism of mechanical-thermally activated DWEMR（MTA-DWEMR）-cement binary system,MTA-DWEMR-slag-cement ternary composite system,mechanical activated DWEMR（MA-DWEMR）-cement-（silica fume）super sulfate cement,MTA-DWEMR-slag-CS super sulfate cement were systematically studied.Finally,the leaching risk and carbon emission reduction potential of the above-mentioned WEMR-based materials were analyzed.The main conclusions are as follows:CS can effectively remove NH₄⁺from EMR and simultaneously solidify heavy metal ions such as Mn²⁺.Mn²⁺is mainly immobilized by Mn Fe₂O₄,Mn₂Si O₄,Ca Mn Si₂O₆,and NH₄⁺escapes as NH₃.Mn²⁺,Cu²⁺,Pb²⁺,and Ni²⁺can also be solidified as hydrated products such as ettringite and C-（A）-S-H gels since it could react with OH^-and CO₃^2-in CS.When used for the disposal of WEMR,CS has dual role of dispersant and disposal agent.Step-by-step dosing and changing of stirring process could promote the chemical reaction between CS and WEMR.When CS dosage is 6%,the leaching concentration of heavy metal ions such as NH₄⁺and Mn²⁺in DWEMR is reduced to lower than the detection limit.Mechanical-thermal activation can improve the pozzolanic activity of DWEMR.The pozzolanic activity of BM3-C7 is better than that of BM3.BM3 dosage in the MA-DWEMR-cement could reach 10%,the fluidity of BM3-10 is 6.10%lower than that of P.I 42.5.3 d and 7 d compressive strength of BM3-10 is comparable to that of P.I 42.5,which at 28 d reaches 50.60 MPa.BM3-C7 dosage in the MTA-DWEMR-cement could reach 20%.The fluidity of BM3-C7-20 is 5.87%lower than that of P.I 42.5,and its compressive strength at 3 d,7 d and 28 d are 21.34 MPa,23.25 MPa and 30.32 MPa,respectively.With the increase of curing age,quartz,gypsum and silicate in the system are gradually consumed,and more hydration products such as ettringite and C-（A）-S-H gel would be generated.The porosity of blended mortar is greater than that of P.I 42.5.Simultaneously,pore structure of blended mortar is optimized.BM3-C7 dosage in the MTA-DWEMR-slag-cement could be 15%.The fluidity of S5-BM3-C7-15 is 207 mm,and its flexural and compressive strength at 28 d are 7.94 MPa and 44.28 MPa.The fluidity of S15-BM3-C7-15 is 191.5 mm,and its flexural and compressive strength at 28 d are 7.73 MPa and 44.23 MPa.The alkali-sulfate synergistic excitation system formed by the ternary composite system can effectively stimulate the activity of slag and BM3-C7 to generate more hydration products such as Ca（OH）₂,ettringite,C-（A）-S-H gel and hydrotalcite.Compared with MTA-DWEMR-cement,the ternary composite cementitious material system has a higher strength and better microstructure.Under the same BM3 dosage,the fluidity of the MA-DWEMR-slag-cement super sulfate cement is 10%higher than that of the MA-DWEMR-slag-cement-silica fume.BM3dosage in the MA-DWEMR-slag-cement super sulfate cement can be 25%,and the flexural and compressive strength at 28 d are 5.96 MPa and 23.32 MPa.BM3 dosage in the MA-DWEMR-slag-cement-silica fume super sulfate cement can be 30%,the flexural and compressive strength at 28 d are 6.32 MPa and 23.51 MPa.The MA-DWEMR-slag-cement-silica fume system shows a better strength and microstructure,because this system generates more hydration products such as ettringite and C-（A）-S-H gel.In the all-solid waste super sulfate cement system,BM3-C7 mainly plays the role of sulfate initiator,and also exerts the pozzolanic characteristics.Anhydrous gypsum could be formed in the hydration products at 1 d,and with the increase of hydration age,anhydrous gypsum in the system is gradually converted to gypsum dihydrate,participated and generated more hydrated products such as ettringite and C-（A）-S-H gel.The pore structure of all-solid waste super sulfate cement is optimized with the increase of BM3-C7 dosage,and the pore structure of CS dosage is not deteriorated by reducing BM3-C7 dosage.When preparing all-solid waste super sulfate cement,the CS dosage is 5%,the BM3-C7 dosage can be 25%;When the BM3-C7 dosage is 15%,3%CS can exert a good alkali excitation effect.Under neutral and acid rain leaching conditions,the WEMR cement-based materials do not have the leaching risk of NH₄⁺,Mn²⁺,Cu²⁺,Pb²⁺and Ni²⁺.BM3-10 and BM3-C7-20have a leaching risk of Cr^6+/3+,while other groups have no leaching risk.The total carbon emissions of cement-based materials of EMR decrease with the increase of BM3 or BM3-C7dosage,and the preparation of cement-based materials from WEMR has a good carbon emission reduction potential.