Available online at http://ijcpe.uobaghdad.edu.iq and www.iasj.net Iraqi Journal of Chemical and Petroleum Engineering Vol.19 No.4 (December 2018) 1 – 11 EISSN: 2618-0707, PISSN: 1997-4884 Corresponding Authors: Aya Abbas Najim, Email: ayaaabbas@yahoo.com, Ahmed A. Mohammed, Email: ahmed.abedm@yahoo.com IJCPE is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Biosorption of Methylene Blue from Aqueous Solution Using Mixed Algae Aya Abbas Najim and Ahmed A. Mohammed Environmental Engineering Department, College of Engineering, University of Baghdad Abstract A mixture of algae biomass (Chrysophyta, Cyanophyta, and Chlorophyte) has been investigated for its possible adsorption removal of cationic dyes (methylene blue, MB). Effect of pH (1-8), biosorbent dosage (0.2-2 g/100ml), agitated speed (100-300), particle size (1304-89µm), temperature (20-40˚C), initial dye concentration (20-300 mg/L), and sorption–desorption were investigated to assess the algal-dye sorption mechanism. Different pre-treatments, alkali, protonation, and CaCl2 have been experienced in order to enhance the adsorption capacity as well as the stability of the algal biomass. Equilibrium isotherm data were analyzed using Langmuir, Freundlich, and Temkin models. The maximum dye-sorption capacity was 26.65 mg/g at pH= 5, 250 rpm, 89µm, 25˚C, and 50 mg/L as initial concentration. Four kinetic models were tested, pseudo first order, pseudo second order, intra- particle diffusion and Elovich model. Taking into account the analysis of the (SSR and X 2 ), the data were best fitted to Temkin isotherm model. The pseudo-second order with higher coefficient of determination fitted the data very well. Thermodynamic parameters (ΓG 0 , ΓH 0 , ΓS 0 , Ea and S*) at temperature ranges of 293–313 K demonstrated that biosorption is an endothermic, spontaneous reaction and higher solution temperature favors MB removal by adsorption onto algae biomass. Results show that adsorption- desorption process lasts for five cycle before losing its efficiency and the recovery efficiency increased up to 80.52%. Keywords: cationic dye, adsorption, desorption, algae, endothermic Received on 20/02/0206, Accepted on 01/00/0206, published on 12/00/0206 https://doi.org/10.31699/IJCPE.2018.4.1 1- Introduction Many industries, such as textiles, plastic, leather, dye manufacturing, sugar manufacturing, carpet, pulp, cosmetic and paper use pigments to color their products ‎[1]. Serious pollution of surface waters, ground waters and soil is caused by the colored effluent discharged by these industries. Among the above cited industries, textile and dye manufacturing industries are the main source of dye contamination that on discharge creates serious environmental problems ‎[2]. Synthetic dyes are dangerous toxic organic compounds which have a major negative environmental impact, and cannot degrade completely due to the presence of the atomic rings that afford high thermal, physiochemical, and optical stability ‎[3], ‎[4]. Therefore the present of these dyes in water is unwanted due to inhibiting photosynthetic action, affects the nature of the water so decrease site value for swimming, boating and fishing, even at low concentrations the physio- chemical properties of the ecosystem are changed and prevent light penetration into water, it is hard to be treated by conventional treatment system. Biodegradation or biological treatment of textile industry dyes is ineffective, time-consuming and very difficult because such dyes must have a high photolytic and chemical stability ‎[5]. Methylene Blue (MB) dye has several side effects such as eye burns, dyspnea, a burning feeling while ingestion through the mouth, vomiting, profuse, plentiful sweating, blood problems, nausea, and mental distraction ‎[5], ‎[6], ‎[7]. Various methods for dye contaminant treatment include ozone treatment, photochemical oxidation, cation exchange membranes, ultrafiltration, nano-filtration, electro-chemical degradation, reverse osmosis, and anaerobic degradation ‎[8]. Nevertheless, those mentioned treatments have many limitations, such as expensive, corrosion, low efficiency, require sensitive operating conditions, consume large amount of energy and chemical reagents, imperfect removal of colored, and produce huge quantity of sludge ‎[3], ‎[9]. Compared to the above cited methods, adsorption has been proven to be more effective, because it offers many benefits such as simple to design, cost effective, non- sensitivity to toxic materials, and easy to operate. Adsorption has some limitations such as problems faced in segregating sorbent from sorbate in order to be regenerated and spent adsorbent may be considered a hazardous waste. Adsorption is traditionally done by using activated carbon. https://doi.org/10.31699/IJCPE.2018.4.1 A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 2 Yet, the high cost of the activation processes limits its usage in wastewater treatment processes, ineffectual against disperse and vat dyes moreover, there is regeneration problems, as well as, after adsorption process it is difficult to separate the treated activated carbon from the bulk solutions ‎[10], ‎[11]. Adsorption is a multi-step process, comprising of four consecutive elementary steps in the case of biomass; the adsorption of solute from solution by adsorbent with pores, the transport of the moving contaminating ions to the outer surface of the biomass (film diffusion), the movement of the solute from the particle surface into interior site by pore diffusion, and finally the adsorption of the adsorbate that takes place into the active sites inside adsorbent particle. The third phenomenon, between these three processes, is take into consideration to be faster and is not the step that limits organic compounds uptake ‎[6], ‎[10]. Over the last decade, many paths have been done to promote inexpensive and effective adsorbents to remove contaminants from a set of starting materials such as agriculture waste and biological material (bacteria, fungi, yeast, algae, and plants) ‎[12], ‎[13]. Algae is one of the most favorable sources of protein supplements, biofuel, biosorbent, and organic fertilizer owing to their advantages like capacity to use fresh, marine or wastewater, reduce greenhouse gas from the environment, do not compete with food yields, and non-requirement of fertile land [14]. It is an efficient biosorbent to be used for dyes removal from wastewaters discharges by industrial activities and gainful, due to the functional groups (amino, hydroxyl, sulfate, and carboxyl) located on the cell surface, which play an active role in the biosorption process ‎[15]. Maurya et al [14] showed that the De-Oiled Algal Biomass DAB (10 g/ L) removes 86% of the dye (50 mg/ L) in 5 minutes under static condition and nearly 100% in 24-hours with agitation at 150 rpm, which indicates the MB removal by DAB in static conditions is more feasible as it requires lesser energy input. The objective of this work is to examine the ability of mixed algae as an adsorbent for the removal of cationic (basic) dye from simulated wastewater under various pH values, algae dosage, contact times, initial methylene blue dye concentrations, temperature, different shaking speed and different algae particles size. Moreover different substances with different concentration for algae pretreatment, and desorption - recovery process by using different concentration of nitric acid to reuse the biomass was also evaluated. Equilibrium and kinetic models were used to estimate the sorption potential and the rate of reaction respectively. 2- Experimental Work 2.1. Preparation of Biomass and Adsorbate Mixed algae consist of (80% Chrysophyta, 5% Cyanophyta, 14% Chlorophyte, and 1% Microscopic animals). These algae were collected from the Tigris River, Iraq. After that, the collected algae was washed many times with tap water to get rid of impurities, dirt and other unwanted materials such as (non-vertebrate animals, small worms, crustaceans, bird feathers), then with distilled water twice to ensure clearness. The washed algae was left under the sun for three days to dry and then dried in an oven (Model: F62700, Barnstead Thermolyne, Germany) at 60°C for 3 h to ensure that the sample is dried completely. The dried algal biomass were cut off, crushed in a mechanical mill and sieved, average size of (1304, 500, 177, and 89) 𝛍m particle diameters. Thirty grams of dried algae biomass 177 µm diameter were treated with 500 ml of NaOH, CaCl2 and HCl for 1 hr at different concentrations (0.05 M, 0.1 M, and 0.5 M), then put in a shaker at 50 rpm for 1 hr to improve the biosorption capacity to methylene blue. The mixture was filtered, washed several times with distilled water till the solution pH value reached 7.0 and then the algal biomass dried at 60 ˚C for a period of 4 hr in the oven. The dye utilized in this study was Methylene Blue (CI 52015; CAS No=7220-79-3; chemical formula: C16H18ClN3S.3H2O; molecular weight = 373.90 g/mole.; minimum assay=99.0%; HIMEDIA), a cationic thiazine. Synthetic aqueous stock solution 1000 mg/l of methylene blue was prepared by dissolving 1.0 g of MB in 1L of distilled water. For all experiments, the concentration of MB was determined by an UV-visible spectrophotometer (Cary-100 conc., Varian, USA) at a wavelength corresponding to the maximum absorbance of the dye solution (λmax= 662 nm), using 0.1 N of NaOH and HCl to get the desired value of the initial pH. HNO3 (0.05M and 0.1) M was used for sorbent desorption. 2.2. Batch Experiments The experiment on the effects of pH was conducted by mix-up 0.5 g adsorbent dosage with 50 ppm of MB solution at different pH (1-8), and then the flasks were shaken at 200 rpm for 2 hr. For studying the influence of various biomass dosages on the MB percentage removal, experiments were conducted by varying the biomass dosage (0.2-2 g/100 ml) with 50 mg/L MB solution. Shaking speed effects on MB adsorption was investigated by using 50 mg/L solution at various shaking speed (100, 200, and 300 rpm) with best values of biomass dosage and pH. To investigate whether particle size (1304, 500, 177, and 89 µm) affected the removal of MB, the experiment was carried out using 50 mg/l of MB solution (pH=5, 7g/L adsorbent, 250 rpm shaking speed, and 120 min shaking time). To study the effect of shaking time and initial MB concentration on the percentage removal, experiments were conducted by mixing 0.7 g/100 ml adsorbent dosage with different MB concentrations (20, 50, 100, 200, and 300 mg/L) for 3 hr. at best conditions obtained from the previous experiment. The impact of the temperature on MB adsorption was studied by changing the temperature (20, 25, 30, 35, and 40) using shaking incubator (ISO 9001, model: LSI-3016A, NO.B110416002, Korea) at the best conditions obtained from the previous tests. A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 3 The results from these experiments were used to calculate the associated thermodynamic parameters. Adsorption–desorption experiments were carried for (0.05 M and 0.1 M HNO3) discretely up to five cycles. A single cycle system is composed of adsorption step (120 min) followed by desorption step (60 min) (pH, 5.0; biosorbent, 0.7g/100 ml; agitation, 250 rpm; dye concentration, 100 mg/l; temperature, 25˚C; adsorption contact time, 120 min; desorption time, 60 min). The dye loaded algal biomass after adsorption, was filtered, dried in air then reintroduced into desorption solvent (0.05 M and 0.1M) HNO3 (0.7 g/ 100 ml, HNO3). The biosorption capacity and removal efficiency were calculated as follows ‎[16]: qe = ( ) (1) % Removal efficiency= ∗100 (2) Where Ci and Ce are the initial and equilibrium dyes concentration in the solution (mg/L), V is the volume of solution in (L), and m the quantity of biomass applied in (g). The eluting efficiencies of the desorbent Ed are expressed as follows ‎[17]: E (%) = x 100 (3) mad: total adsorbed quantity of MB, mg/l , md :the MB mass desorbed, mg/l 3- Results and Discussion 3.1. FT-IR Analysis The purpose behind the FTIR analysis is to identify the different functional groups found in algae that's responsible for the adsorption process and to pin point the changes that take place in the algae biomass structure ‎[18]. Fig. 1 shows the results of the notice IR absorption frequencies in different regions for algae before and after biosorption of MB. The peaks show in the FTIR spectrum were allocated to several functional groups according to their own wave numbers. The band at 3700-3000 cm -1 is O-H and N-H stretching of (alcohols, phenols, and carboxylic acids), and 3400-3200 cm -1 is stretching of polymeric compounds; 2962-2853 cm -1 interval is stretching vibration of C-H especially alkyl chains, intense band at 2000-2500 cm -1 interval for carboxylic acid, 1720-1431 cm -1 interval for the presence of amide, carboxylates, sulfonates, and ketone groups. The C-O, C-C, C-OH stretching vibration referred to peaks in the region of 1359-1041 cm - 1, while bands in the fingerprint regions (900–750 cm −1 ) referred to the aromatic –C–H groups. From Figure 1, we noticed that after biosorption of the dye molecules, a shifting or disappearance of some peaks as well as the emergence of new ones. The reason behind these shifts is the binding process that occurs on the surface of the biomass. (a) (b) Fig. 1. FTIR peaks of transmittance of MB, (A) before adsorption, (B) after adsorption 3.2. Effect of pH The pH is a significant feature impacting the adsorption studies. This was because pH effects the function groups on the biomass surface and determines dye solubility in the aqueous solution ‎[19]. Dependence of organic and inorganic biosorption on pH is associated to both the ionization state of functional groups of the adsorbent which affects the availability of binding sites and the contaminants chemistry (complexation by organic and/or inorganic ligands, hydrolysis, precipitation and redox reactions) in the solution ‎[20]. The effect of solution pH on the sorption of dyes on the sorbent was studied by altering the pH in range (1-8). The increase in pH cause an increase in percentage sorption as depicted in Fig. 2. The minimum sorption was observed at low pH (pH= 1.0-4.0) due to the existence of higher H + ion concentration which is favored sorption in comparison with other cationic pollutants. At higher concentration of H + ions, the biomass surface will be farther positively charged thus reducing the attraction force between adsorbent and cation pollutant ‎[16]. At pH values (5–8), the removal percentage of dye was almost constant. A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 4 The solute (dye ions) uptake can be related to the chemical structure of the solute in the solution and also to the active sites located at the biomass surface. The removal percentage of methylene blue (MB) reaches maximum at pH 5, no significant altered beyond pH 5 was observed because when pH is high, the adsorbent particles surface may be negatively charged causing the enhancement the cationic dyes through electrostatics forces of attraction. Fig. 2. pH effect on the removal efficiency of MB (m=0.5 g/100 ml, Ci= 50 mg/l, T= 25˚C, 89µm, speed= 200 rpm, and time=120 min) In general non- treated algal biosorbent has alkali and alkaline earth metals such as Na + , Mg 2+ , K + and Ca 2+ which are essentially tied to the acid functional groups of the algae and were attained from sea water [20]. The pH and EC were measured at different time intervals during the agitation process. Fig. 3 shows the increase in the electrical conductivity (EC) and pH values with time. In this case, the cations of light metals were being eluted from the algal biomass during the experiments, while the cationic dyes were being sorbed onto the biomass. It was noticed that the solution final pH was greater than the initial value, attributed to ion exchange mechanisms, hence, the witnessed release light metals well-adjusted the uptake of cation. Accordingly, the light metals released, when algae biomass reacts with the cationic pollutants causing an increase in the pH as a result of formation of light metal alkalis [21]. Fig. 3. pH and EC evolution as a function of time dyes biosorption, (m=0.7 g/100 ml, T=25˚C, Ci= 50 mg/l, 89 µm at 200 rpm) 3.3. Effect of Biomass Dosage The doses (mass) of adsorbent effects on the adsorption of MB are shown in Fig. 4. The biomass dosage is an important parameter used to determine the capacity of biosorbent for specific initial concentration ‎[3]. In this paper different amount of algae biomass (0.2-2 g/ 100 ml) were used. An increasing amount of algal biomass may be able to fully adsorb the pollutants or reach an equilibrium state when reaching a plateau at a fixed concentration of each pollutant ‎[3], ‎[11]. It is obviously noticed that the removal percentage of MB increases from 61.94 to 92.43%, as the algae dosage increases from 0.2 to 0.7 g. After some point (above 0.7 g), adsorption removal efficiency was steady credited to a screen effect between adsorbent ‎[21], or the observed behavior occurred because at the initial stage there were sufficient binding sites for the complexation of dye molecules and increasing the dose beyond 0.7 g resulted in the establishment of equilibrium between the cationic dyes bounded to biosorbent and those remaining un-adsorbed in the mixture ‎[12], or because high adsorbent amounts are known to cause agglomeration and accordingly reduce the distance between biomass leading to protecting the binding sites from contaminants ‎[10]. Increasing biomass concentrations results in increases final bio-removal although it has negative effects on biosorption capacity because fixed initial concentration leads to unsaturated active site on biomass surface and the increase in the biomass concentrations cause particle aggregation ‎[3]. Fig. 4. Effect of sorbent amount on the removal efficiency of MB by algae biomass (pH 5, T= 25˚C, Ci=50 mg/l, 89 µm, speed = 200 rpm and time=120 min) 3.4. Effect of Shaker Speed With suitable agitation speed, the resistance of mass transfer can be reduced. The solution rate of diffusion (from the bulk liquid to the liquid boundary layer surrounding particles) becomes higher because turbulence improves and the liquid boundary layer thickness is reduced, as a result of increasing the agitation rate ‎[13]. Shaker speed affects the spreading of dye molecules in solution and also disrupts the film resistance surrounding the adsorbent particles by influence the uptake of dye molecules. 0 20 40 60 80 100 0 2 4 6 8 10 R e m o va l% pH A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 5 When speed of the shaker increased from 100 to 300 rpm, the time required to achieve equilibrium was reduced, so the available biomass surface area increases due to the deficiency of aggregation of the biosorbent that finally leads to rapid adsorption of MB ‎[14]. Furthermore, these results obviously show that 250 rpm is adequate to gain maximum percentage removal of MB as shown in Fig. 5, no significant altered beyond this point was observed because the solution has reached equilibrium. Fig. 5. Effect of shaker speed on the removal efficiency of MB (pH 5, m= 0.7 g/100 ml, T= 25˚C, Ci= 50 mg/l, 89 µm, and time=120 min) 3.5. Effect of Particle Size of Biomass Surface area of the biomass is a key parameter for sorption. Fig. 6 shows the relationship between the size of sorbent particle and the removal efficiency. The results show an adverse relation between the removal efficiency and particle size, the former increase with later decrease. The higher sorption level attained by the smallest sorbents particle size connected to the notation that smaller particle sizes provide large surface areas and exhibit faster adsorption more than that of sorbents with lower surface area. The removal efficiency decreased from 93.19 to 66.82 % as the particle size increased from 89 to 1304 µm. Fig. 6. Effect of particle size diameter of sorbent on the removal effeciency of MB (pH 5, m= 0.7 g, T= 25˚C, speed= 250 rpm, Ci= 50 mg/L, and time=120 min) The diffusional resistance to mass transfer is greater for large particles, but the smallest size allows very fast removal kinetics if the adsorption is to be primarily a surface phenomenon ‎[8]. There is a tendency as fine particles takes lesser time to equilibrium in shorter time. 3.6. Effect of Initial Concentration with Time The initial concentration of MB affords a main driving force to outweigh all mass transfer resistance between the aqueous and solid phases ‎[8]. The experiments were performed at distinct initial MB concentrations (20 to 300 mg/L). From Fig. 7 it notes that the percentage removal decreases from: 98.97 to 65.48%, as the initial concentration increased from 20 to 300 mg/L. One of the most essential parameters affecting the biosorption efficiency, modeling and designing the adsorption process in the industry is the contact time. It was inferred that the amount of MB adsorbed was fast for the first 15 min and after that, a slower pace (15–60 min) for the range 20-100 mg/L, (15-120 min) for 200-300 mg/L, and finally reached saturation. The available sites saturation occurs much earlier when the solution contains a higher initial dye concentration, resulting in a solution with high dye content at equilibrium ‎[14]. It can be seen that the percentage removal was not altered significantly when the concentration increased from 20-50 mg/L because the dosage of algae may have sufficient sites that can be exchanged for the above mentioned range. However, by increasing concentrations to 100, 200 and 300 mg/L, a sharp reduction in percentage removal was obvious due to insufficient exchangeable sites in the biomass to accumulate these concentrations. Pirbazari et al ‎[10] show that 80 min duration is the contact time was needed for MB solutions with initial concentrations of 50–200 mg/L to reach equilibrium. Fig. 7. Effect of initial concentration with time on the removal efficiency of MB (pH 5, m= 0.7 g, 25˚C, speed= 250 rpm, 89 µm, and time=180 min) 3.7. Effect of Temperature and Thermodynamic Parameter: Temperature has a vigorous influence on adsorption process as it can affect the process by an increase or decrease in the amount of adsorption. A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 6 Yu and Luo, ‎[9] show that temperature is an essential factor for the real application of MAC as most of the textile dye effluents are produced at relatively high temperature. The results are plotted in Fig. 8 and the values of thermodynamic parameters are tabulated in Table 1 which shows the adsorption efficiency of MB onto algae biomass at five different temperatures of 20, 25, 30, 35, and 40 o C. It can be seen that with increasing temperature the percentage removal increases, suggesting that endothermic nature of the process. This effect may be due to the fact that at higher temperature, an increase in active sites occurs due to bond rupture ‎[10], or an increasing of the surface area available for the sorption because pores in algae were enlarged, penetration of contaminants within the pores of algae, diffusion, and the equilibrium capacity of the adsorbent will be modified for a particular adsorbate ‎[9]. The removal efficiency increase as temperature increase till it reaches 40˚C. At higher temperature, texture of biomass was changed, as a results damaging and reduce number of functional groups, that’s why temperature was limited to 40˚C ‎[18]. Fig. 8. Effect of temperature on the removal efficiency of MB (pH 5, m= 0.7 g, Ci= 50 mg/l, speed= 250 rpm, 89 µm, and time=120 min) A linear plot with intercept of ln S*and slope of Ea/R will be observed by plotting (1−θ) against 1/T. The positive values of ΓH° and Ea reveal that: adsorption is endothermic and higher solution temperature favors MB removal by adsorption on algae biomass ‎[3]. Similarly, the ΓS° values are positive indicating increasing in randomness at the solid/ solution interface during their sorption. The negative values of ∆G at all temperatures range studied showed that the process is spontaneous with high affinity of MB to dried algae ‎[3]. The value of sticking probability S* is found very close to zero indicating that the adsorption process follows chemisorption [10]. ( ) ( ) (4) ΓG= ΓH- ΓST (5) KC = (6) S* = (1 − θ) exp - ( ) (7) θ = (1 – ) (8) Where: Kc stands for the equilibrium constant, Cad stands for the adsorbed concentration of MB on the adsorbent per liter of the solution at equilibrium (mg.l -1 ), Ce is the equilibrium concentration of MB in the solution (mg.l -1 ), ΓH° stands for the biosorption process enthalpy (kJ/mole), R stands for the universal gas constant (8.314 J/mole. K), ΓS° stands for the biosorption process entropy (J/K. mole), ΓG stands for the Gibbs free energy of biosorption (kJ/mole), T stands for the solution temperature (K), θ is surface coverage, S* is sticking probability, and Ea is activation energy. Table 1. The thermodynamic parameters for the sorption of MB on algae biomass T(K) ∆G o (kJ/mol) ∆S o (J/mol K) ∆H o (KJ/mol) Ea (kJ/mol) S* 071 -5.558 190.615 50.2922 47.645 2.986E-10 076 -6.511 121 -7.464 126 -8.417 101 -9.370 3.8. Desorption The recyclability of an adsorbent is of fundamental importance in industrial practice for pollutant removal from wastewater ‎[22]. Desorption of the adsorbed MB from the tested algae biomass were studied in a batch system. The dye adsorbed onto biosorbent was eluted with various concentrations of nitric acid. More than 80% of the adsorbed MB was desorbed from the biosorbent by using 0.1 M HNO3 in the first cycle. If desorbent achieves the assigned standards, it is promising to recover the adsorbate in concentrated form and to regenerate the biosorbent in order to use it in another biosorption cycle. In order to show the reusability of algae biomass, adsorption- desorption cycle of pollutants was repeated five times by using the same preparations. The recovery percentages using two concentrations of HNO3 from algae biomass are calculated from Eq. (3). Nitric acid was used for this purpose because at acidic condition the adsorbent surface protonate by replacing the adsorbed pollutants on the adsorbent surface leading to desorption of positively charged pollutants or due to the fact that most biosorption exhibit an ion-exchange mechanism for cations and thus increasing the acidity of species loaded algae leads to leaching of cations pollutants from biosorbent ‎[23]. The sorption process of contaminants is not completely reversible due to diffusion of trace contaminants within oxide particles or into micro pores, incorporation of contaminants into oxides, precipitation, re-adsorption, and chemisorptive adsorption of contaminants onto adsorbent hinders the desorption of contaminants from the spent biomass ‎[24]. A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 7 He et al., ‎[5] used acetonitrile to desorbe methylene blue from Nano-crystalline Cellulose, the results show that only 18% of MB was desorbed so acetonitrile was not very effective. Nevertheless, more than 90% removal after 7 desorption cycles was achieved by using ethanol. The results of adsorption- desorption processes are shown in Fig. 9. Fig. 9. Five cycle of adsorption- desorption for MB with two different concentration of HNO3 (pH 5, m= 0.7 g, Ci= 100 mg/l, 89 µm, speed= 200 rpm, T= 25 ˚C, adsorption time=120 min, and desorption time= 60 min) 3.9. Results of Pretreatment Treated biosorbent generally involves one of two chemical modifications. The first, the biosorbent is interacted with a high concentration of a given ion in aqueous solution consequently, the majority of the sites are occupied by, materials such as calcium, sodium, or potassium. The second is protonation of the biomass with a strong acid such as HCl, so the proton transfers the light metal ions from the binding sites ‎[21]. The most common algal pretreatments are NaoH, CaCl2, HCl, formaldehyde, and glutaraldehyde ‎[25]. In this review, algae biomass was treated with sodium hydroxide (0.05, 0.1, and 0.5) M, calcium chloride (0.05, 0.1, and 0.5) M, and hydrochloric acid (0.05, 0.1, and 0.5) M to improve the biosorption capacities to methylene blue dye. From Fig. 10, the modification of algae biomass by chloride calcium has removal efficiency lower than NaOH but better than HCl, the adsorption efficiency decreased with the strength of the acidity. Alkali treatment with NaOH creates additional basic sites for binding MB cations while acid-treated bleaching earth is a better adsorbent for reactive dyes and acid dyes than for basic dyes ‎[26]. Lignocellulosic materials treatment with sodium hydroxide can cause a decrease in crystallinity, a decrease in the degree of polymerization, swelling which leads to an increase in internal surface area, separation of structural linkage between lignin and carbohydrates, increase in the amount of galactouronic acid groups after hydrolysis of O - methyl ester groups, removes natural fats and waxes from the cellulose fiber surfaces thus revealing chemically reactive functional groups like – OH, and disruption of the lignin structure, the decrease in copper removal at high NaOH concentration, due to the destruction of biomass. For the adsorption of cationic dyes, the surfaces of biomass must be negatively charged. Pretreatment by chloride calcium causes calcium binding to alginate that plays a significant role in ion exchange. To increase the contaminants removal efficiency by algae biomass, CaCl2 consider a cost- effective treatment ‎[25]. Although acid modification decrease organic content (lignin, and hemicellulose) of adsorbent and increase porosity, positively charged surfaces with hydrogen ions prevented to extra increase of adsorption ‎[19]. Fig. 10. Modification of algae biomass using different concentrations of NaoH, CaCl2, and HCl to remove dyes from solution (pH 5, m= 0.6 g, Ci= 50 mg/l, 177 µm, speed= 200 rpm, and time=120 min) 4- Biosorption Isotherm and Kinetics Models A very essential tool for the investigation of sorption process is sorption isotherms. Establish the connection between the amount of adsorbate adsorbed and the equilibrium concentration at a constant temperature by the unit weight of adsorbent. Langmuir, Freundlich, and Temkin isotherm models are widely used to study the sorption process. The model parameters can be construed further, providing understanding of sorption mechanism, surface properties, and an affinity of the sorbent. The Langmuir adsorption has been the most widely used adsorption isotherm for the adsorption of a solute from a liquid solution ‎[1]. A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 8 The Langmuir model assumes a monolayer adsorption of solutes onto a surface comprised of identical sites with homogeneous biosorption energy ‎[3]. The multilayer sorption and the sorption on heterogeneous surfaces model by using the Freundlich equation ‎[7]. Temkin isotherm has a factor that obviously taking into the account of adsorbent–adsorbate interactions. The model presumed that the heat of adsorption (function of temperature) of all molecules in the layer, by ignoring the extremely low and large values of concentrations, decreases linearly rather than logarithmic with coverage ‎[27]. The experimental data was analyzed by using non-linear isotherm models. The non- linear isotherm model parameters were evaluated by using Microsoft Excel SOLVER software. These models are plotted in Fig. 11, tabulated in Table 2 and the results are shown in Table 3. It can be seen that Temkin model has the higher coefficient of determination R 2 . The biosorption kinetics is very important to study the removal of contaminants from wastewater, as it offers valued insights into sorption reaction mechanism and the reaction pathways ‎[28]. Pseudo- second- order model better fits the experimental data compared to the pseudo- first- order model, particle diffusion model and Elovich model according to higher value of correlation coefficient (R 2 ). This means that biosorption of MB occurs in a monolayer on the surface of adsorbent. The rate limiting step may be chemical sorption according to the second order kinetic model assumption ‎[5]. The results are shown in Table 4, figures not shown. Table 2. Equations for the sorption isotherm and kinetics models Model Equation used Reference Langmuir Isotherm qe = [27] Freundlich Isotherm qe = K Ce 1/n [27] Temkin isotherm qe =BT ln KT Ce BT = , [27] Pseudo-first-order ln (qe-qt) = ln qe – k1 t [3] Pseudo-second- order ( ) [3] Intra- particle diffusion qt = kpt 1/2 + C [4] Elovich model qt= ln(αβ)+ ln(t) [29] Sum square error (SSE) ∑(qe,calc-qe,meas) 2 [30] Nonlinear chi- square test (X 2 ) ∑ ( ) [30] Where, qe is the sorbed dyes molecules on the adsorbent (mg g -1 ), qm is the maximum sorption capacity for monolayer coverage (mg g -1 ), b is the affinity of the binding site (L mg -1 ), and Ce is MB concentration in the solution at equilibrium (mg L -1 ). Kf = constant indicative of the relative adsorption capacity of the adsorbent (mg/g), 1/n = constant indicative of the intensity of the adsorption. kT is Temkin sorption potential (L mg -1 ), and BT & bT are Temkin constants. qt is MB uptake capacity (mg/g) at any time t; k1 is the pseudo-first-order rate constant (1/min); and k2 is the pseudo-second-order rate constant (g/mg. min), Kp (mg/g min 0.5 ) is the intra-particle diffusion rate constant, C is the value of intercept that gives an idea about the boundary layer thickness. α is the chemi- sorption rate (mg/g. min) and β is a coefficient in relation with the extension of covered surface and activation energy of chemi-sorption (g/mg). Fig. 11. Isotherm data of MB adsorption onto algae biomass (pH=5; shaking speed=250 rpm, initial dye concentration =50 mg/l, 89 µm, and 25˚C) Table 3. Parameters of isotherms model for sorption of MB Type of isotherm parameters values Langmuir qm (mg/g) 26.65 b (l/mg) 0.0685 R 2 0.9493 RL 0.226 Sum square error SSE 6.908 X 2 2.1949 Freundlich Kf 2.388 n 1.5699 R 2 0.9429 Sum square error SSE 7.794 X 2 2.6931 Temkin KT (l/mg) 0.695 BT 5.7149 R 2 0.955 Sum square error SSE 6.0597 X 2 1.6221 A. A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 9 Table 4. Parameters of kinetic models for sorption of MB Kinetic models Parameters 20 ppm 50 ppm 100 ppm 200 ppm 300 ppm Experimental qe 2.8277 6.7134 12.511 22.391 28.063 Pseudo first order qe 0.129 0.476 1.447 5.092 6.980 K1 0.0153 0.017 22200 2220 0.0163 R 2 225032 22632 22747 229322 0.8804 Pseudo second order qe 2.827 6.725 12.56 22.57 28.17 K2 0.558 22037 22230 22200 8E-3 R 2 0.9999 0 0.9999 22777 0.9979 Intra-particle diffusion C 2.65 6.102 11.02 17.35 21.13 KP 222022 22230 22000 2217 0.51 R 2 22542 22660 22737 227724 0.9863 Elovich model α 2.2E21 1.45E14 124.58E9 428679.8 271798.3 β 20.24 5.875 2.531 228118 0.631 R 2 226544 227471 227711 227411 0.9207 5- Conclusions The results indicated that algae biomass could be used as an efficient biosorbent material for the removal of methylene blue dye molecules from aqueous solution. The higher percentage achieved (98.97%) at pH 5, 0.7 g /100ml biomass dosage, 250 rpm shaking speed, 89 µm particle size, 20 ppm initial dye concentration, and T=25˚C for 120 min. Temkin model fitted the experimental data very well compared to Langmuir and Freundlich models, while the kinetic study well fitted by pseudo second order with very high R 2 . The thermodynamic parameters calculated (ΓG°, ΓH° and ΓS°) showed that the biosorption of MB were feasible, spontaneous and endothermic at temperature ranges of 293-313 k. Results show that adsorption- desorption process lasts for five cycle before losing its efficiency and the recovery efficiency increased from 50.7% to 80.52% when the concentration of nitric acid increased from 0.05 to 0.1M. Treated algae with NaOH show the highest removal efficiency compared to CaCl2 and HCl in all its concentrations. Nomenclature B: Affinity of the binding site, L/ mg, BT & bT: Temkin constants C: Value of intercept that gives an idea about the boundary layer thickness, mg/g Cad: Adsorbed concentration, mg/L Ce: Concentration at equilibrium, mg/L Ci: Initial concentration, mg/L Ea: Activation energy, KJ/ mole EC: Electrical conductivity, µs/cm ΓG: Gibbs free energy, KJ/mole ΓH: Enthalpy change, KJ/mole k1: Pseudo-first-order rate constant, 1/min k2: Pseudo-second-order rate constant, g/mg. min KC: Equilibrium constant Kf: Constant indicative of the relative adsorption capacity of the adsorbent, mg/g Kp: Intra-particle diffusion rate constant, mg/g min 0.5 kT: Temkin sorption potential, L/ mg m: Mass of adsorbent, g mad: Total adsorbed, mg/L md: Desorbed concentration, mg/L 1/n: Constant indicative of the intensity of the adsorption qe: Sorbed dyes molecules on the adsorbent, mg/ g qm: The maximum sorption capacity for monolayer coverage, mg/ g qt: MB uptake capacity, mg/g at any time t R: Universal gas constant S*: Sticking probability ΓS: Entropy change, J/K. mole T: Temperature, K V: Volume, L Θ: Surface coverage Α: Chemisorption rate, mg/g. min Β: Coefficient in relation with the extension of covered surface and activation energy of chemisorption (g/mg) References [1] O. 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A. Najim and A. A. Mohammed / Iraqi Journal of Chemical and Petroleum Engineering 19,4 (2018) 1-11 00 المائي باستخدام الطحالب المختلطةامتزاز صبغه المثيل الزرقاء من المحلول الخالصة ( Chlorophyte، و Chrysophyta ،Cyanophytaتم استخدام خميط من الكتمة الحيوية لمطحالب ) جم / 2-0.2( ، كمية المادة المازة )8-1(. تم دراسة تأثير األس الهيدروجيني )MBالزاله )الصبغه الزرقاء ، -20ميكرو متر( ، درجة الحرارة ) 88-1304( ، حجم الجسيمات )300-100)مل( ، سرعة التحريك 100 40˚C( تركيز الصبغة األولي ، )ممغم / لتر( ، وتمت دراسة امتصاص االمتصاص لتقييم آلية 300- 20 من أجل CaCl2امتصاص صبغة الطحالب. وقد تم تجربة مختمف المعالجات، القمويات ، والبروتونات ، و االمتزاز وكذلك استقرار الكتمة الحيوية لمطحالب. تم تحميل بيانات متساوي الحرارة باستخدام نماذج تعزيز قدرة Langmuir وFreundlich وTemkin ممغ / غم عند 26.65. كانت السعة القصوى المتصاص األصباغ ممغم / 50ية ، و درجة مئو 25ميكرو متر ، و 88دورة في الدقيقة ، و 250، و 5الرقم الهيدروجيني = لتر كتركيز أولي. تم اختبار أربعة نماذج حركية ، من الدرجة األولى الزائفة ، والنظام الثاني الزائف ، وانتشار ( ، كانت البيانات األفضل X2و SSR. مع األخذ بعين االعتبار تحميل )Elovichداخل الجزبئة والنموذج نتائج ان البيانات تخضع لمودبل الزائف من الدرجة الثانية. . اضهرت الTemkin isothermمالئمة لنموذج *( عند درجات حرارة تتراوح بين Sو ΓG0 ،ΓH0 ،ΓS0 ،Eaأظهرت المعممات الديناميكية الحرارية ) 283-313 K أن اإلمتصاص هو تفاعل ماص لمحرارة ، وتفاعل تمقائي ، ودرجة حرارة أعمى لمحل تدعم إزالة االسترجاع تستمر -الصبغة الزرقاء باالمتزاز عمى الكتمة الحيوية لمطحالب. تظهر النتائج أن عممية االمتزاز ٪. 80.52لمدة خمس دورات قبل أن تفقد كفاءتها وزيادة كفاءة االسترداد إلى