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International Conference on Multidisciplinary Research & Practice P a g e | 540 Preparation of Wollastonite from Used of and Quartz through Solid-State Reaction #1 #2 #3 D.Thenmuhil , K.V.Vignaswaran , R.Yasmin Sulthana , T.Pavithra#4

#Department of Ceramic Technology, A.C. College of Technology, Anna University, Chennai-25,

Abstract— Wollastonite (CaSiO3) was produced using solid- studies, silicate materials produced from a mixture state reaction from used Plaster of Paris and quartz as starting of and silica sand are found to possess bioactive materials. Plaster of Paris from recycled molds serves as the properties in a simulated body fluid solution environment, source for and quartz was used as the source of silica. The especially the silicate chains wollastonite (CaSiO3) ratios of plaster of Paris and quartz used were taken as 2:1, 3:1 o o and (CaMgSi2O6).In the present study, attempt was and 4:1 and firing was carried out at 1200 C, 1300 C and made to produce wollastonite material using waste plaster of 1350oC. The raw materials and fired products were characterised for mineral phases, chemical composition of Paris and quartz as a waste management process. A solid- state technique with various plaster of Paris/quartz ratios content such as CaO, SiO2 and loss on ignition (LOI), density and microstructure. CaSiO3 with an α-phase was detected at namely 2:1, 3:1, 4:1 and different firing temperatures like firing temperatures 1350oC with 3 h soaking obtained from a 1200oC, 1300oC and 1350oC were employed for producing 2:1 ratio. No α-CaSiO3 was detected for 3:1 and 4:1 ratios. wollastonite materials. The phases present and microstructures of the final fired materials are reported. Keywords— Plaster of Paris, Quartz, Wollastonite, Solid-state reaction. II. EXPERIMENTAL WORK

The sequence followed for the preparation of I. INTRODUCTION wollastonite is illustrated in the Fig.1 alcium silicate is an industrial material that has many uses in industries, but the most important applications C Raw materials are in building materials such as glass, cement, bricks and tiles for roofs, fireproof ceilings and building board. consists of four types of compound, i.e. monocalcium silicate (CaSiO ), dicalciumsilicate (Ca SiO ), tricalcium 3 2 4 Weighing silicate (Ca SiO ) and tricalcium disilicon heptaoxide 3 5 (Ca Si O ), all of which are obtained by reacting various 3 2 7 molar ratios of (CaO) / dioxide (SiO ), 2 namely1:1, 2:1, 3:1 and 3:2. Mixing Wollastonite, also known as monocalcium silicate

(CaSiO ), has been synthesized using a few techniques such 3 as precipitation, sol-gel, solid-state reaction, etc.

Precipitation is the most frequently used technique, with Drying sintering temperature between 900◦ and1250◦C, which produces the amorphous β-phase of wollastonite[4-8]. Production of β-wollastonite using solid-state reaction has been reported by several researchers [4,9]. They used reagent Firing grade limestone and natural silica sand as raw materials with a sintering temperature of 1400◦C for 2 h. De la Casa-Lillo et Fig 1 Flow sheet for preparation of wollastonite al. [10] used the sol-gel technique to produce wollastonite and obtained a stable phase of α-wollastonite The raw materials taken in this work are used Plaster of Paris (pseudowollastonite) at 1400◦C. and quartz. Plaster of Paris was obtained from the waste Plaster of Paris is used mainly in construction and in ceramic molds. Both the raw materials were sampled and medical . Plaster of Paris used as molds have a short ground separately by planetary mill to obtain finer particle durability because they tend to react with water. Also when it size, i.e. of 100% passage through a ~70-µm sieve. is stored for a long time in open atmosphere they react with Calcium silicate material was prepared from a atmospheric moisture and get hardened. So a considerable mixture of plaster of Paris and quartz via the solid-state amount of plaster of Paris is wasted. Therefore, it is essential reaction according to the following equation. to reduce the wastage of plaster of Paris. To the best of our knowledge, plaster of Paris has not been used as lime source CaSO4+SiO2 CaSiO3+SO3 to produce wollastonite materials. According to previous

Volume I Issue VIII IJRSI ISSN 2321-2705

International Conference on Multidisciplinary Research & Practice P a g e | 541

Plaster of Paris/quartz molar ratios of 2:1, 3:1, 4:1 and firing temperatures of 1200°C, 1300°C, 1350°C were used in this study. Each sample is varied with soaking time of 1hour, 2hours, and 3hours respectively. The mixed powder was placed in a box furnace and heated at a rate of 5°Cmin-1. The heated sample is then cooled to room temperature and ground to obtain fine powders. A total of 27 samples were prepared. The raw materials and final products were characterised for phase identification using X-ray diffractometry(XRD), analysis of CaO was done using titrimetric method and SiO2 by gravimetric method and loss on ignition(LOI) content by the wet loss technique. Density was measured using pycnometer and morphology was examined using a scanning electron (SEM). Fig 2 XRD pattern of Quartz and Plaster of Paris

III. RESULTS AND DISCUSSION

A. Characteristics of raw materials:

Fig 2 shows the XRD pattern of the raw materials and consists of calcium sulphate from Plaster of Paris and 99% silica from quartz; calcium sulphate has orthorhombic structure and silica has hexagonal structure. The results of CaO, SiO2, LOI and density are tabulated in Table 1.The obtained CaO(32%) and SiO2(99%) contents show that the Plaster of Paris and quartz used in this study were from high grade materials. The LOI content of the used Plaster of Paris of 45.6% and quartz 17% revealed the decomposition of carbonates from Plaster of Paris and also showed that elimination of volatile matter, such as water of hydration and organic materials, had occurred [15]. The obtained Plaster of Paris had a density of 2.59 g/cm3and quartz of 2.65 g/cm3, which are close to their typical densities of 2.62 g/cm3 and 2.66 g/cm3, respectively [1,3].

TABLE 1-CaO,SiO2, LOI and density of raw materials. Fig 3 SEM images of Plaster of Paris and Quartz. Materilas CaO SiO2 LOI Density (%) (%) (%) (g cm−3) Plaster 32 - 45.6 2.59 Fig 3 shows the SEM micrographs of Plaster of Paris and of Paris quartz after the grinding process.

Quartz - 99 17 2.65 B. Characteristics of fired product: a. XRD

The fired samples were characterized by Scanning Electron Microscope (SEM) and X-Ray diffraction (XRD). All the 27 samples with 3different firing temperature and each soaked for 3 different times were characterized by SEM and XRD. Of the various firing temperatures and soaking times, the sample prepared with plaster of Paris/quartz taken in 2:1 ratio, fired at 1350oC and soaked for 3 hours (Sample ID. W21C3) was found to result in better formation of wollastonite as observed from the XRD pattern given in Fig 4. The XRD patterns obtained for the sample prepared with plaster of Paris/quartz taken in 3:1 ratio, fired at 1300oC and soaked for 3 hours (Sample ID. W31B3) and the sample prepared with plaster of Paris/quartz taken in 3:1 ratio, fired o at 1350 C and soaked for 3 hours (Sample ID. W31C3) are given in Fig 5 and Fig 6 respectively for comparison.

Volume I Issue VIII IJRSI ISSN 2321-2705

International Conference on Multidisciplinary Research & Practice P a g e | 542

In this study, the α-CaSiO3 phase was observed at 1350oC for the stoichiometric mixture of Plaster of Paris and quartz of 2:1 proportion. A few mineral crystalline phases, such as portlandite [Ca(OH)2], (CaSiO4) and olivine [Ca2(SiO4)] can be obtained at particular firing temperatures. The formation of larnite and olivine is in agreement with the work done by chen et al.[16],and wesselsky &Jensen[17].

b. LOI AND DENSITY The purity of calcium silicate produced was influenced by the chemical reaction between Plaster of Paris and quartz that occurred at each firing temperature. Nevertheless, the LOI content was more affected by the decomposition of Plaster of Paris and the removal of volatile materials produced from the firing process. The main component of LOI are shown in the Fig.7.Density of the fired products at a molar ratio 2:1increased with temperature Fig. 4 XRD Pattern of W21C 3 and was highly influenced by the sintering temperature and purity of raw materials, Plaster of Paris and quartz [20].At 1350°C. α- CaSiO3 was produced with a density approaching its typical density of 2.86-3.09 g/cm3 [21].

Fig. 5 XRD Pattern of W31C3

Fig.7. LOI content of the final products after firing at different firing temperatures for molar ratio 2:1

C.SEM The SEM image of W21C3 is shown in Fig. 8.Only in this composition the morphology of obtained α- CaSiO3 showed needle-like structure.

Fig. 6 XRD Pattern of W31B3

It can be observed from the XRD pattern that W21C3 shows a better result in concern with the calcium silicate material. It is noted that after the firing process, X- ray patterns showed that all of the final products were in the crystalline phase.

Fig 8 SEM micrograph

Volume I Issue VIII IJRSI ISSN 2321-2705

International Conference on Multidisciplinary Research & Practice P a g e | 543

IV. CONCLUSION

Calcium silicate material was successfully synthesized from plaster of Paris and quartz using a solid- state reaction. The wollastonite phase was fully obtained at a

Plaster of Paris/Quartz molar ratio of 2:1, sintered at 1350°C for 3 h, with a dense microstructure. Purity of the raw materials, molar ratio of plaster of Paris/quartz and firing temperature all had an influence on the final product of calcium silicate materials. The study shows that the preparation of wollastonite can be from used Plaster of Paris.

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Volume I Issue VIII IJRSI ISSN 2321-2705