ABSTRACT
Significant interest in waste-cement recycling has been stimulated because of the high contents of calcium and silicon in waste cement. The reactivity of calcium and silicon in the raw material is one of the important factors for the hydrothermal synthesis of xonotlite. Therefore, the effect of the reactivity of calcium and silicon in the waste cement on the hydrothermal synthesis of xonotlite was studied in this paper. Portland cement that was hydrated for 6 months, with the aim of simulating the waste cement, was used for the first time as the calcium and silicon source in the hydrothermal synthesis of xonotlite. As calcination would raise the reactivity of the hydrated cement, the effect of calcination of the Portland hydrated cement on the hydrothermal synthesis of xonotlite was investigated. The hydrated cement was calcined at 900 °C, and the hydrothermal synthesis was carried out at 220 °C for different times. The phases of the hydrothermal products were analyzed by XRD and TG-DSC, and it was noted that the calcination of hydrated cement affected the formation rate of xonotlite. The content of xonotlite increased from 18% (synthesized with hydrated cement without calcination) to 74% (synthesized from hydrated cement with calcination at 900 °C) during a reaction time of 24 h. Furthermore, the micromorphologies of xonotlite using calcined and hydrated cement were compared and discussed from the perspective of the reactivity of the starting materials.
ABSTRACT
Lead-zinc tailings are generated during the mining process which is considered as hazardous solid waste due to its high heavy metal content and leachability in the natural state. At present, the most effective technology for disposing heavy metals in solid wastes is the solidification/stabilization (S/S) technique. In terms of S/S technology, chemical stabilization is one of the most potential and practical method. This paper aims to investigate the S/S property of four typical chemical agents (Na2S, NaH2PO4, TMT and Na2EDTA) on the heavy metals in lead-zinc tailings. The results reveal that the heavy metals lead and zinc in tailings are stabilized more effectively by using chelating agents TMT than by using inorganic chemical agents Na2S and NaH2PO4. When the dosage of TMT reaches 4%, the leaching concentration of lead and zinc is 0.18 and 14.60â mg/L according to toxicity characteristic leaching procedure (TCLP), and the stabilization efficiency of lead and zinc is 99.31% and 80.92%, respectively, while the leaching concentration of lead and zinc just drops to 0.41 and 16.00â mg/L with addition of 10% NaH2PO4. Furthermore, the leaching concentration of heavy metal lead in tailings treated by 4% Na2EDTA increases to 53.44â mg/L which far exceeds the standard of pollution control. Therefore, considering stabilization efficiency and dosage, TMT is the preferred agent for solidifying heavy metals in lead-zinc tailings.
Subject(s)
Metals, Heavy , Zinc , Edetic Acid , Lead , Metals, Heavy/analysis , Solid Waste , Zinc/analysisABSTRACT
Additions of andalusite aggregates (19 wt%) were shown in previous literature to enhance the antioxidation of Al2O3-SiC-C (ASC) castables. This work aims to investigate whether micronized andalusite has a greater influence on antioxidation improvement than andalusite aggregates. Various low contents (5 wt% and below) of micronized andalusite (≤5 µm) were introduced as a substitute for brown fused alumina in the matrix of ASC castables. The antioxidation of castable specimens was estimated by the oxidized area ratio on the fracture surface after a thermal shock test. The microstructure and phases of micronized andalusite and the castable specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results suggest that the antioxidation effects of ASC castables with a low addition of micronized andalusite are effectively enhanced. The heat-induced transformation of andalusite produces SiO2-rich glass, favoring the sintering of the castable matrix and impeding oxygen diffusion into the castable's interior. Therefore, the castable antioxidation is enhanced without deteriorating the hot modulus of rupture.
ABSTRACT
High temperature melting treatment and cement solidification are technologies currently used to reduce the leaching of heavy metals in municipal solid waste incinerator (MSWI) fly ash. In this paper, to ascertain the feasibility of melting MSWI fly ash with blast furnace (BF) slag, ultra-risk MSWI(U-MSWI) fly ash having high heavy metal (Zn, Pb, Cu, and Cr) contents were blended with BF slag, then melted and quenched into water to prepare reconstructed slag. The melting and solidification behaviors, phase composition and microstructure, and heavy metal leachability of reconstructed slag were studied. In addition, to study the further solidification and utilization of reconstructed slag in cement, the compressive strength and leaching concentration of cement composites with reconstructed slag were also investigated. The results indicate that the presence of heavy metals in the U-MSWI fly ash had a little influence on the microstructure and phase composition of reconstructed slag. The leaching concentration of heavy metals in the reconstructed slag increased with the increasing of U-MSWI fly ash content, and when the content of U-MSWI fly ash was less than 50 wt%, the reconstructed slag could meet the environmental requirements. The reconstructed slag further solidified by cement could be applied to landfill and construction materials. The technology of melting reconstruction treatment with cement solidification was a technical-economical choice for the industrial treatment of U-MSWI fly ash.
Subject(s)
Metals, Heavy/analysis , Refuse Disposal , Carbon , Coal Ash , Construction Materials , Incineration , Particulate Matter , Solid WasteABSTRACT
RATIONALE: Compressive myelopathy and compression fracture of aggressive vertebral hemangioma after parturition is a rare condition. Vertebral body compression fracture and high serum progesterone lead to extraosseous hemangioma enlargment cause narrowing the spinal canal which contribute to compressive myelopathy relate to pregnancy. PATIENT CONCERNS: We report a case of compressive myelopathy and compression fracture of aggressive vertebral hemangioma after parturition in a 35-year-old woman. The patient complained unable to walk and experienced intense pain in the back. DIAGNOSIS: Based on the clinical features and imaging studies, the patient underwent a T4-T6 laminectomy. Histopathology consistent with vertebral hemangioma. INTERVENTIONS: The patient underwent laminectomy for decompression. After subperiosteal dissection of the paraspinal muscles and exposure of the laminae, there was no involvement of the lamina by the tumor. The epidural tumor was removed through the spaces lateral to the thecal sac. Vertebroplasty was performed through T5 pedicles bilaterally and 7âml of polymethylmethacrylate (PMMA) cement was injected. T4-T6 pedicle screw fixation was performed for segmental fixation and fusion. OUTCOMES: Six months after resection of the tumor the patient remained asymptomatic. She reported no low back pain and had returned to her normal daily activities, with no radiographic evidence of recurrence on MRI. Physical examination revealed that superficial and deep sensation was restored to normal levels in the lower extremities. LESSONS: The occurrence of compressive myelopathy of pregnancy related vertebral hemangiomas is quite unusual. It can lead to serious neurologic deficits if not treated immediately. So, prompt diagnosis is important in planning optimal therapy and preventing morbidity for patients.
