Influence of the Processing Route on Reliability of Raschig Rings for Wastewater Treatments

Abstract

Ceramic Raschig rings are used as fillers in the columns for wastewater treatment to immobilise heavy metals in polluted waters. Their effectiveness is determined by properties such as porosity and specific surface area. Therefore, microstructural control during processing is necessary to assure uniform performance of random packed columns filled with Raschig rings. In this work, Weibull statistics of the stress to fracture of rings placed under diametrical compression loading is proposed as a method to compare reliability of the rings.Three green processing methods, uniaxial pressing, extrusion and slip casting, have been used to obtain rings using industrial and urban wastes as raw materials (diatoms from beer industry, sludges from paper industry and animal bones). Significant differences between the Weibull parameters for the three series of the same material were found indicating that the most reliable processing route was extrusion. The same analysis was done for uniaxially pressed rings containing hydroxyapatite as single-phase. In spite of differences between the actual strength values, Weibull parameters were coincident for both uniaxially pressed series.

Application of hydroxyapatite and cement kiln dust mixture in adsorption of lead ions from aqueous solution

“…In spite of the excellent adsorption properties of HAp, the mechanical strength of this material which is synthesized using calcium hydroxide is usually low to fabricate the packed beds [15,16]. Furthermore, the addition of other reinforcement materials such as quartz significantly decreases the sorption capacity.…”

“…Villora et al have been considered the effect of shaping method on the compressive strength and reliability of Raschig ring formed by extrusion, slip casting and pressing processes [16]. The rings produced by the extrusion method were recognized to show the maximum strength and Weibull modulus.…”

“…Regardless, the sorption capacity and compressive strength, the manufacturing process should provide the reliable beds. In principle the reliability of beds can be presented by the probability function proposed by Weibull that describes the failure occurring from the critical flaws [15,16].…”

Influence of sintering temperature on microstructural changes of ceramic Raschig ring

“…During the firing of this body a considerable amount of liquid phase is formed, which diffuses by capillary force into the fine pores of solid and reduces the porosity and specific surface area. These transformations of texture cause significant changes in mechanical, thermal and chemical characteristics of pieces determining the properties of ceramic Raschig rings, which relate to shrinkage, water absorption and mechanical strength that define packing quality [6,7].…”

Corrigendum to “Deviations from Weibull statistics in brittle porous materials” [Acta Mater. 61 (2013) 7207–7215]

“…, / -ROR [3], J -BOR [4], I -DC [5], N -4PB for P = 46% and C for P = 40-41% [6], and . -SST [7]; alumina  -4PB [8], titanium dioxide -3PB [9], niobium and tantalum doped zirconia þ -3PB [10], 75 mol% NiO-YSZ à -ROR [11], NiO-TZ3Y + T1 } -BOR [12], NiO-TZ3Y + T2 r -BOR [12], NiO-TZ3Y + CF É -BOR [12], MgAl 2 O 4 à -4PB [13]; Ce 0:9 Gd 0:1 O 1:95 purple , Ce 0:8 Gd 0:2 O 1:90 green , YSZ sintered at 1300°C red , YSZ sintered at 1350°C orange , La 0:85 Sr 0:15 MnO 3 brown , 75 mol% NiO-YSZ blue , 3 mol% Y 2 O 3 -ZrO 2 magenta -ROR [14].…”