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Synthesis and Characterization of Zeolite Nay Using Local Rice Husk as a Source of Silica and Removal of Cr(vi) from Wastewater by Zeolite

A. K. Ghosh
Department of Chemistry, Jahangirnagar University, Savar, Dhaka, Bangladesh

S. Ahmed
Institute of Glass and Ceramic Research and Testing (IGCRT), Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka-1205, Bangladesh

M. Y. A. Mollah
Department of Chemistry, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The Zeolite NaY in pure phase was synthesized from rice husk (RH) following a three step synthetic route. In the preliminary step seed gel was prepared from a mixture of silicate and Na-acetate solution. This step was then followed by the preparation of feedstock gel. The third or final step involved the mixing of seed gel (5%) and feedstock gel (95%) which produced the zeolite of desired phase, NaY. The synthesized zeolite was characterized by FT-IR, XRD, SEM and DLS particle size analyzer and used to treat wastewater containing Cr (VI). The adsorption of Cr(VI) was monitored as a function of pH of the solution, contact time and initial concentration of Cr(VI). The adsorption results revealed that after scaling up the methodology, the synthesized zeolite NaY could be used as a promising cost-effective adsorbent for the treatment of wastewater containing chromium.

Keywords: Rice Husk; Silica; Aluminosilicate; Zeolite NaY; Chromium

Location: Department of Chemistry, Jahangirnagar University, Savar, Dhaka

Start Date:

End Date:

Program Area: Socio-economic and Policy

Non-commodity: Performance

Objectives:

An attempt has been made to remove chromium (VI) from waste water using the zeolite, synthesized from RHA. Such an attempt is expected to be beneficial in two ways: (i) A cost effective and easy approach will be facilitated to remove Cr(VI) from tannery wastewater and (ii) utilization of RHA will be a promising material recycling technology for future waste management.

Methodology:

Chemicals: Analar grade NaOH, NaAlO₂, K₂Cr₂O₇ were purchased either from BDH, UK or E. Merk Germany and used as received. RH was collected from Biswas Rice Mill, Sutrujitpur, Magura. All the solutions of desired concentrations were prepared using double distilled water. Method: The experimental method comprised the following three steps: (a) Preparation of amorphous Si from RH; (b) Synthesis of zeolite, NaY using prepared silica (Si); and (c) Treatment of wastewater containing chromium using the synthesized zeolite NaY. (a) Preparation of amorphous Si from RH: Prior to burning, the rice husk was washed three times by distilled water and then soaked in 1% H₂SO₄ for 24 hours. Rice husk was then washed repeatedly with distilled water to remove acid and it was dried at normal temperature and pressure. The dried rice husk was then burnt in a Tube Furnace at a constant temperature of 650^oC under usual atmospheric pressure for an hour to ensure that the product is in amorphous silica phase. The product was obtained in the form of blackish powder. It was then further burnt in a Muffle Furnace at 650^oC for six hours to obtain the white ash. The rice husk ash was ground using a mortar to homogenize and to obtain a powdered form of the material. (b) Synthesis of zeolite, NaY using prepared silica Sodium aluminate, sodium hydroxide (NaOH) pellets and silica from RHA were used as the raw materials to synthesize zeolite NaY. The synthesis was accomplished by following the method of Ginter, D. M. (Ginter et. al., 1992) but the compositions and types of raw materials were different. The overall method comprised three steps; at first seed gel was prepared which was followed by the second step feedstock gel while the final step was the preparation of overall gel. Preparation of seed gel: Seed gel was prepared from a mixture of aluminate and silicate solution. At first NaOH solution was prepared by dissolving a requisite amount of the pellets in deionized water. This NaOH solution was then mixed with the sodium aluminate, NaAlO₂ solution to prepare the aluminate solution. The mixture was then heated gently under continuous stirring condition until it turned into solution. On the other hand, silicate solution was prepared by dissolving the silica (obtained from RHA) in NaOH solution. It was then stirred and heated in the water bath maintaining the water at boiling temperature. The aluminate and silicate were then mixed in a Teflon beaker and stirred until it became homogeneous. At this stage, the mixture was transferred into an airtight Teflon bottle and kept for ageing at room temperature for 24 hours. After 24 hours of ageing, the loose brown gel appeared which was used as seed gel. Seed gel contributed 5% of the overall gel composition. Effect of adsorbent-solution contact time: Six reagent bottles were charged with 50 mL Cr (VI) solution of 10 mg L-1 concentration and the pH of each sample was adjusted at 2.0. A fixed amount (0.5 g) of zeolite NaY was added to each bottle and shaken well at room temperature. After different time intervals (0, 10, 30, 60, 180 and 360 min), the reaction mixtures were separated by filtering and the concentrations of residual Cr (VI) in the supernatant solutions were measured by the AAS. Effect of initial Cr(VI) concentration: Effect of initial Cr(VI) concentration on the removal of Cr(VI) was investigated at room temperature with initial concentrations of Cr (VI) as 2.0, 11.0, 21.0 and 106.0 mg L-1 using 0.5 g zeolite NaY as adsorbent. The pH was adjusted at 2.0. The adsorption was allowed for 180 mins. Effect of pH: The effect of pH was studied by varying the initial pH ranges from 2.0 - 7.0 by adjusting the pH with 0.1 M NaOH and 0.1 M HCl. A fixed amount (0.5 g) of the synthesized zeolite NaY was added to 50 mL Cr (VI) solution having the desired pH. The concentration of each Cr (VI) solution was maintained at 10 mg L-1. The solutions were shaken well in the reagent bottles and after 60 min each of the reaction mixture was filtered. The concentration of Cr(VI) in the filtered solutions were measured by AAS.

Source of Information: Bangladesh J. Sci. Ind. Res. 48(2), 81-88, 2013

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Amorphous RHA was produced by controlled burning of rice husk and this amorphous RHA was used to synthesize zeolite NaY following the seed gel and feedstock gel methods. The adsorption efficiency of the prepared zeolite NaY was investigated by treating the synthetic waste water containing chromium. The adsorption results revealed that after careful manipulation of the morphology, particularly the size of the zeolite as well as forming composite with other materials and methodology, zeolite NaY could be used as a promising cost-effective adsorbent for the treatment of waste water containing chromium. However, development of zeolite NaY from RHA will be beneficial in many ways, such as: i. A cost effective and easy approach will be facilitated to remove Cr(VI) from tannery wastewater. ii. Utilization of RHA will be a promising material recycling technology for future waste management. iii. Pure silica produced from RHA could be used for the production of value-added materials (e.g. electronic devices, solar cells etc.) as well as in material science and environmental remediation.

Knowledge Management: Journal