Mechanism of Pore Formation in Novel Porous Permeable Ceramics Prepared from Steel Slag and Bauxite Tailings

Abstract

Porous permeable ceramics (PPC) were prepared from composite ceramsites (CC) via a single firing process. CC were granulated with steel slag as a core and bauxite tailings in an outer-layer. XRD, SEM, EDS, mercury porosimetry and metallographic microscopy were used to study its properties and the pore formation mechanism. Results showed that during sintering process, gradual diffusion of cations from slag to tailings layers enhanced bonding among CC with formation of new crystals: anorthite and pyroxene. PPC had a wider distribution of pores from 0-300 μm sintered at 1 160°C. With an increase in sintering temperature, ceramics were densified with disappearance of the small pores, which had an increasing threshold diameter values from 45 μm at 1 180°C to 70 μm at 1 190°C. Big pores larger than the threshold values would be remained and enlarged due to shrinkage of CC during the densification process. The decreasing amounts of pores and an increasing pore diameter had contrary effects on its permeable properties. PPC sintered at 1 180°C with porosity of 27.5% and medium pore diameter of 92.7 μm had the optimum properties with bending strength of 10.92 MPa, water permeability of 0.039 cm/s and qualified leaching properties of harmful elements (Mn, Cr, V and Pb). This study would promote a more feasible and economic method for producing porous permeable ceramics and improving added value of steel slag and tailings.

Generation of Pyroxene-Based Porous Ceramics from Steel Refining Slag

“…(2) The porous ceramics made from slag were sintered by solid-state processing that involved phase transformation from low-density raw material (2.10-2.90 g/cm 3 ) to highdensity pyroxene (3.22-3.88 g/cm 3 ). The volume shrinkage associated with the phase transformation was confined to the micro reaction areas due to the limited diffusion of cations in the solid state, thereby resulting in the formation of more pores.…”

“…(Received on February 5, 2021; accepted on April 5, 2021) In this paper, porous ceramics were prepared by controlling the composition and sintering temperature of raw materials based on slag from steel refining operations and without the need for a pore-forming agent. Solid-state processing included a phase transformation from low-density raw materials (2.10-2.90 g/cm 3 ) to high-density pyroxene-based ceramics (3.22-3.88 g/cm 3 ). Phase transformations and densification of porous ceramics were investigated by means of mercury intrusion, XRF, SEM and EDS.…”

“…A number of studies have been conducted to explore methods for using the slags produced under oxidizing conditions. Examples include: recovery of iron from steelmaking slags, 1) use as raw material for glass and ceramic industries, 2,3) road and hydraulic construction, 4) fertilizers and soil improvement. 5) The slag, as a by-product generated from refining processes conducted under reducing conditions, which is defined as steel refining slag in this work, contains more CaO (45 wt.%-55 wt.%) than normal steelmaking slag (about 40 wt.%CaO and a certain amount FeO), and is hard to reuse in the cement or concrete industries due to its instability derived from α-Ca 2 SiO 4 , free CaO and free MgO.…”

Permeable Brick Material and Process Selection Based on Sponge City Construction

“…Yu Li [19] and other scholars used composite ceramsite as raw material to prepare porous permeable ceramics by one-time firing process. The steel slag is used as the core, and the bauxite tailings is the outer layer, and the composite ceramsite is granulated.…”