Removal of direct blue 71 from aqueous solution by adsorption on rice husk carbonclinoptilolite composite adsorbent Mohamad Anuar Kamaruddin1, Mohd Suffian Yusoff1, Hamidi Abdul Aziz1, Rasyidah Alrozi2 1
School of Civil Engineering, Universiti Sains Malaysia, 14300, Nibong Tebal, Penang, Malaysia 2 Faculty of Chemical Engineering, Universiti Teknologi MARA Pulau Pinang, Malaysia Email:
[email protected]
Abstract- The adsorption performance of rice husk carbonclinoptilolite (RHC-clinop) for the removal of Direct Blue 71 (DB71) in batch mode was investigated. The RHC-clinop was prepared by pre-determined mixes of clinoptilolite (clinop), rice husk carbon (RHC), and ordinary Portland cement (OPC). The OPC was used as binding agent. The adsorption experiments were conducted at different conditions of adsorbent dosage (0.21.2g), solution pH (2-12) and initial concentration (25-400 mg/L). DB71 adsorption uptake was found to increase with increase in initial concentration and contact time. The optimum adsorption of DB71 was favorable at pH 10 with adsorbent dosage of 1.0g. The experimental data was fitted well with Freundlich isotherm. Adsorption kinetic was found to follow the pseudo-second-order kinetic model with good correlation. The result indicates that the RHC-clinop is suitable for the removal of azo dye by adsorption process.
I. INTRODUCTION In the last decade, various types of dyes have been invented and utilized for a wide range of applications including, textile fabrics, paper printing, hair colorant and coating industries. Dyes consist of complex substantial aromatic compound which can be identified by their variant color, solubility and chemical composition. Extensive application of dyes during product manufacturing generates large amount of colored waste water that caused severe impacts to environmentally sensitive ecosystem including surface and ground water. As a matter of fact, even low concentrations of colored waste water are aesthetically unpleasant and may retarding biological process to some organisms due to the obstruction of sun light penetration [1]. In fact, the excessive uses of azo dyes revealed that some of them and their reaction products such as aromatic amines are highly carcinogenic which make the removal of dyes before disposal of the wastewater is required [2]. Adsorption has been proven as one of the ultimate methods in waste water treatment technologies worldwide. Numerous investigations on the adsorption application for the dye removal in aqueous solution also have been reported elsewhere [3-6] which emphasizes on the utilization of industrial by product [7-9], agricultural waste [10-13],
municipal waste [14, 15] and natural resources [16, 17]. This technique is highly recommended due to the low starting cost, simple handling procedure and requires smaller area at waste water treatment facilities. However, most of the media used in filtration process tends to dissolve or dissolute and forming sludge, sediment, or supernatant at the final stage of the treatment process. Therefore, additional process is required to recover the spent media for the regeneration. Generally, the smaller the particles of adsorbent or catalyst, the better its properties are, but the more difficult the recovery is [18]. In recent years, there are growing interests on the usage of composite materials derivative with special consideration for the removal of pollutants from industrial effluent. Composite materials consist of several types of adsorbents, which have been developed for improving adsorptive properties or producing low-cost adsorbents. By modifying the chemical properties of individual precursor, the latter are more superior in water purification process in terms of improving mechanical strength [19], better adsorption capacity [20], higher cation exchange capacity and easier to regenerate [21]. Accordingly, composite materials that have been investigated in the past years including AC/ferrospinel composite [22], magnetic cellulose/Fe 3 O 4 /activated carbon composite [23], humic acid immobilized-polymer/bentonite composites [20], chitosan and activated clay composite [24], Polyaniline/chitosan composite [25] and carbon mineral composite were successfully produced. In this work, a rice husk carbon-clinoptilolite (RHC-clinop) composite adsorbent was synthesized from two major sources which were rice husk carbon (RHC) and clinoptilolite (clinop). Rice husk is the byproduct from rice milling process, usually applied as a source for steam burner material or as cement replacement during concrete production. Considering it availability, which can be obtained at minimum cost and highly abundant, the RHC usefulness as starting material in composite derived process is highly regarded. Clinop, which is naturally occurrence material, is rich with cations of Sodium (Na) and Potassium (K). They are available either naturally or from synthetically. In Malaysia, clinop is mainly employed as
a fertilizing agent to increase crops yield. Clinop also has been used as a soil treatment to remediate nutrient in soil after harvesting period. In water purification process, Clinop can be a useful material for composite derived process due to its aluminosilicate framework, exchangeable cations, and zeolitic water [26]. Ordinary Portland cement (OPC) was used as a binding agent for hardening the precursors at pre-fixed amount of water binder ratio during mixing process. Direct Blue 71 (DB71) dye was used to appraise the adsorption performance of the prepared composite adsorbent based on the dosage, initial dye concentration and pH solution. Isotherm data was analyzed and assessed with the Langmuir and Freundlich models, respectively. II. MATERIALS AND METHODS A. Composite adsorbent preparation The starting materials were milled using stainless steel mill for 10 hours. The ground samples were sieved with 150 µm sieve aperture prior to mixing process. The sieved products of RHC were undergone cleansing and rinsing process several times using distilled water in order to remove dirt and impurities and followed with oven dried at 105°C. The starting materials were mixed in a mixer and incorporated into a composite with the inclusions of OPC as the low cost binder. A mechanical stirrer (Ika, Germany) was used to well stirred the starting materials to homogenous form by a pre-assigned mixing rate. The water cement ratio was fixed at 30% of total design mix during composite adsorbent preparation. Next, mechanical extruder (Milker, China) was used to extrude the prepared composite adsorbent into desired media size for batch experiment. In order to improve the surface characteristics, the prepared composite adsorbent was subjected to thermal treatment at 105 °C in a convection oven (Memmert, Germany) for 24 hours. B. Adsorbate Direct Blue 71 (DB71) supplied by Sigma Aldrich (M) Malaysia was used as an adsorbate. DB71 dye has a chemical formula of C 40 H 28 N 7 NaO 13 S 4 with molecular weight of 965.94 g/mol. Deionized water supplied by USF ELGA water treatment system was used to prepare all the reagents and solutions. C. Effect of adsorbent dosage The effect of RHC-clinop composite dose on the amount of DB71 adsorbed was obtained by contacting 150 mL of DB71 solution with initial concentration of 100 mg/L with different amount of RHC-clinop into a number of 250 mL erlemenyer flasks at temperature of 30 °C and at pH 6-7. The flasks were placed in a thermo-controlled shaker-incubator (Protech, Malaysia) and agitation was provied at 130 rpm. The equilibrium was obtained when the DB71 solution shows uniform reduction with respect to colour assays. D. Effect of solution pH The effect of pH on the removal of DB71 was analyzed over the pH range of 2-12. The pH of the dye solution was adjusted
by the addition of 0.01M NaOH or 0.01M HCl. A pH meter (Eutech, Singapore) was used to measure the required pH of the solutions prepared. 150 mL of DB71 solution with initial concentration of 100 mg/L was agitated with 1.0 g of RHCclinop composite adsorbent. E. Equilibrium studies Batch experiment was performed by using 5.0 g of RHCclinop and 150 mL of DB71 solution in 250 mL erlenmeyer flasks. Different concentrations of DB71 at 25, 50 100, 200 and 400 mg/L were used to investigate the removal pattern of DB71. The flasks were agitated at 150 rpm for 360 minutes until equilibrium was attained. In order to ensure satisfactory agitating process, the flask lid was wrapped with laboratory film (Parafilm M, USA). All experiments were performed in triplicate and the produced results were tabulated from the means of three different experimental values. At equilibrium, the amount of DB71 adsorbed onto composite media (q e ) was calculated by:
where C o and C e are the liquid-phase concentration of DB 71 dye at initial and at equilibrium, respectively. V (L) is the volume of the DB71 solution and W is the mass of the composite media (g). The percentage removal of dye was calculated as follows:
F. Kinetic studies Adsorption kinetic experiments were conducted by contacting 150 mL of DB71 with initial concentration ranging from 25 to 400 mg/L with 1.0 g of RHC-clinop in 250 mL erlmenyer flasks. In this study, 1.0 g of RHC-clinop was used in each of the flasks and agitated at 150 rpm. The flasks were withdrawn from the shaker at required time intervals and colour was measured, respectively. III. RESULTS AND DISCUSSIONS A. Effect of adsorbent dosage The removal pattern of DB71 towards dosage of the RHCclinop composite adsorbent is shown in Fig. 1. Generally, the influences of adsorbent dosage to the adsorbate are an important parameter in determining its adsorption capacity for a given initial concentration. Fig. 1 shows that the adsorption of DB71 increased gradually from 0.2 to 0.6 g whereby sharp increased was observed from 0.8 to 1.0g. The percentage removal of DB71 was observed increased from 20% to 85%, respectively. This phenomenon could be attributed by greater surface area and availability of more adsorption sites [27]. The removal of DB71 reduced when the dosage was increased from 1.0 g to 1.2 g. Increasing dosage of RHC-clinop composite adsorbent may be retarding the availability of
composite active sites whereby the overlapping or aggregation of the adsorption sites may hindered further reduction of color concentration. B. Effect of solution pH The effect of solution pH of RHC-clinop composite adsorbent on the DB71 removal at initial concentration of 100 mg/L is shown in Fig. 2. The DB71 removal was found to increase uniformly when the solution pH increasing from 2 to 8. The maximum DB71 removal of 90% was achieved at pH 8. Increasing the solution pH was found to significantly affect the adsorption of the DB 71 onto RHC-clinop composite adsorbent. Since DB71 is largely contains with negatively sulfonated compound, it repelled by the negatively charged of clinop ions. Thus, the adsorption of DB71 during acidic condition (pH1), linear (R L =1), favourable (0
