The Preparation Of Copper Slag-based Phosphate Cementitious Materials And The Basic Research On Solidifying Electrolytic Manganese Slag

In recent years,China's manganese industry has developed rapidly,and has become the largest producer,consumer and exporter of electrolytic manganese in the world.Its production capacity and output account for more than 95%of the world's total.The electrolytic manganese residue?EMR?is the acid waste residue produced in the production of electrolytic manganese metal.It has small particles and high moisture,and the content of soluble manganese?Mn?and free ammonia nitrogen?NH₄⁺-N?seriously exceeds the standard.The EMR is the biggest and most dangerous pollution source in the electrolytic manganese industry.Due to the limitation of technical reasons,EMR is mainly treated by open-air storage of slag reservoir in China.During long-term storage,high concentration of manganese ions and NH₄⁺-N enter the soil and rivers with leachate,causing serious harm to the surrounding environment.Therefore,the harmless treatment of EMR becomes the primary choice for the treatment of EMR.In this thesis,The EMR from an electrolytic manganese plant in Tongren,Guizhou Province was taken as the research object.On the basis of in-depth discussion of its physical and chemical properties,the preparation of copper slag-based phosphate cementitious materials by using copper slag?CS?and sodium dihydrogen phosphate?P?was proposed,and solidification of EMR with admixture.The X-ray diffractometer?XRD?,scanning electron microscope?SEM?and Fourier transform infrared spectroscopy?FT-IR?were used to characterize the cementitious Materials and EMR solidified body.The formation mechanism of copper slag-based phosphate cementitious material and the solidification reaction mechanism of EMR.The research results and conclusions are as follows:?1?The mineral composition of EMR shows that the crystalline form of EMR is better,mainly containing CaSO₄·2H₂O and SiO₂,Mn and NH₄⁺-N mainly exist in the formofMnSO₄·2H₂O,?NH₄?₂SO₄,?NH₄?₂Mn?SO₄?₂·6H₂Oand?NH₄?₂Mg?SO₄?₂·6H₂O.The toxicity leaching of EMR showed that the leaching concentration of Mn²⁺and NH₄⁺-N was the highest,1082.43 mg/L and 396.76 mg/L,respectively,which were 541 and 26 times higher than the limit value of GB8978-1996"Comprehensive Wastewater Discharge Standard".?2?The preparation scheme of copper slag-based phosphate cementitious material was determined by experiments.When m?CS/P?is 3:1 and water-cement ratio is 0.11,the compressive strength of cementitious materials is the highest.The compressive strength of 1,3,7 and 28 days was 26.9,33.6,36.1 and 42.0 MPa respectively,and the setting time was 5.0 min.The results show that borax,boric acid and sodium tripolyphosphate all have retarding effect on the cementitious materials,but boric acid and sodium tripolyph osphate inhibit the development of compressive strength.When the borax content is 0.5%,the compressive strength of the cementitious materials is significantly increased.The compressive strength of the cementitious materials at 1,3,7 and 28 days is 34.4,36.3,39.9 and 47.2 MPa respectively,and the setting time is 8.35 min.?3?The results of XRD,SEM and FT-IR characterization analysis show that:The main hydration cementitious phases of copper slag-based phosphate cementitious materials are FeH₂P₃O₁₀,Fe?H₂PO₄?₃,Fe?PO₃?₂,Fe?PO₃?₃,Fe₅P₄O₂₀H₁₀,Mg₃?PO₄?₂,Mg?H₂PO₄?₂,etc.The cementitious phases of the system are cemented with each other and tightly connected with unreacted substances to form a whole,which improves the compactness of the material and has a certain compressive strength.?4?The copper slag-based phosphate cementing material and the admixture synergistically solidify EMR results show that:When m?CS/P?is 3:1 and MgO content is 5%,the solidification effect of EMR is the best.Among them,the maximum solid capacity of A is 65%.Under these conditions,the compressive strength of solidification body for 1,3,7 and 28 days is 9.0,13.4,17.1 and 20.3 MPa,respectively.The leaching concentration of manganese ion is 1.15 mg/L and that o f NH₄⁺-N is 14.81 mg/L,which meets the requirements of GB 8978-1996"Comprehensive Wastewater Discharge Standard".?5?XRD,SEM and FT-IR characterization of EMR solidification body showed that the reaction mechanism of solidified EMR is complex.Manganese ions and NH₄⁺-N in the solidified body are chemically precipitated by forming a phosphate having a low solubility,such as Mn₃?PO₄?₂,MnPO₄·1.5H₂O,Mn₃?PO₄?₂·1.5H₂O,NH₄FePO₄·H₂O and NH₄MgPO₄·6H₂O et al.At the same time,copper slag-based phosphate cementitious materials can also be physically sealed by physical encapsulation and physical adsorption,so that the solidification body has high compactness and mechanical properties.Copper slag-based phosphate cementitious material was used to solidify EMR.The harmless treatment of EMR was realized by chemical precipitation,physical encapsulation and physical adsorption.