Iraqi Journal of Chemical and Petroleum Engineering Vol.18 No.2 (June 2017) 69 - 81 ISSN: 1997-4884 Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent Raghad F. ALmilly and MOHANNED H. HASAN Chemical Engineering Department, College of Engineering, University of Baghdad Email: rfkalm@yahoo.com and mhh1970m@yahoo.com Abstract Effluent from incompetent wastewater treatment plants (WWTPs) contains a great variety of pollutants so support water treatments are essential. The present work studies the removal of phosphate species from aqueous solutions by adsorption on to spherical Calcined Sand -Clay mixture (CSCM) used a natural, local and low-cost adsorbent. Batch experiments were performed to estimate removal efficiency of phosphate. The adsorption experiments were carried out as function of pH, dose of adsorbent, initial concentration, temperature and time of adsorption. The efficient removal was accomplished for pH between 10 and 12. The experimental results also showed that the removal of phosphate by (CSCM) was rapid (the % removal 98.9%, 92%, 90%, 89% in 60 min) when the initial phosphate concentrations were at 5, 10, 15, 20 mg/l, respectively at optimum PH 10-12 and optimum dose was 5 gm/200ml. The adsorption process is time dependent. Thermodynamic studies showed that phosphate adsorption was exothermic. The effect of temperature range of 15-30 °C has been investigated. The results indicated that the temperature significantly affected phosphate adsorption on (CSCM) adsorbent. Langmuir and Freundlich isotherms models indicated that both isotherms were proper to describe the adsorption characteristics of (CSCM), with Langmuir being more fit. Adsorption capacity of phosphate had equal to 0.835 mg phosphorous/g adsorbent. The study reveal that calcined sand-clay mixture is an excellent low cost material for phosphate removal in wastewater treatment process . Key words: Adsorption, Wastewater, Phosphate, Calcined sand-clay mixture. Introduction Environmental problem has a serious consequences on public health due to inefficient treatment of domestic, municipal and industrial wastewater. Nutrient discharged in the surface water and ground water bear a great deal of responsibility on water bloom and eutrophication that adversely affects on surface water [1]. The concentrations of phosphorus between 3 and 15 mg/L mostly brought together from domestic and industrial wastewaters [2]. According to the requirement of American state environmental agencies and the U.S. Environmental Protection Agency (EPA) the total phosphorus effluent concentrations from dischargers must University of Baghdad College of Engineering Iraqi Journal of Chemical and Petroleum Engineering mailto:rfkalm@yahoo.com mailto:mhh1970m@yahoo.com Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent 70 IJCPE Vol.18 No.2 (June 2017) -Available online at: www.iasj.net be as far as 0.05 mg/L to deal with water quality problems [3] . Biological, chemical, or combined biological and chemical processes are common methods for phosphorus removal performance. A specific group of polyphosphate - accumulating microorganisms play a great deal of consuming excessive phosphorus as intracellular storage through biological treatment, and then phosphorus is removed from the liquid by sludge wasting. Chemical phosphorus technique is established to precipitate phosphate as form of sparingly soluble metal phosphate complexes by adding salts of multivalent metal ions (e.g. FeCl3, Fe2(SO4)3, Al2(SO4)3, or Ca(OH)2). Biological and chemical processes are similar in target to take out only soluble orthophosphates or transform those forms in the influent into ortho-P during the treatment process then in to solids phase by subsequent solid and liquid separations. Once P effluent level observed within permitted limits indicate both the effectiveness of chemical and/or biological P treatment processes in achieving goals as well as efficient final solid and liquid separation [4]. Adsorption has been tested as an alternative to conventional method for phosphate removal in wastewater treatment for a long time. For several reasons, inorganic adsorbents are offered to use as promising alternative [5]. Adsorption process was chosen especially for some advantages such as less production of sludge and easy operation, but it has not been applied widely since the suspended solids contained in the feed water accumulate in and clog the adsorbent bed and most adsorbents cannot be reused [6]. Various adsorbents were improved for phosphate removal such as alum sludge [7], red mud [8], fly ash [9], calcite [10], dolomite mineral [11], Clay soil [12], Bentonite Clay [13], The purposes of this study were to determine the following: (1) the feasibility of using calcined sand- clay mixture (CSCM) to adsorb phosphate; and (2) the optimal conditions of using calcined sand-clay mixture for phosphorus removal. Material and Method Adsorbate Synthetic Phosphate stock solutions were prepared in the laboratory by dissolving an amount of anhydrous potassium dihydrogen phosphate KH2PO4 (0.2195 g) in 1 liter distilled water. Further dilution was conducted on the stock solution to get the desired concentrations of the experimental solutions using distilled water. To determine Phosphate concentration the Vanadomolybdo phosphoric Acid Colometric Method was followed with a UV–Vis spectrophotometer and measured at 470 nm according to [14]. Adsorption Media (Adsorbent Preparation) Sand and clay materials have been brought from the sea of Najaf region and mixed at different volume percent ages to form spherical particles about 10 mm in diameter by hand. After that they have been dried and then calcined at 800 C to prevent their dissolution in the water. Chemical Properties The chemical analysis of the adsorption media was achieved using (XRF) in the University of Baghdad / College of Science /Department of Geological Survey and Mining. The results of the composition of each material used in this study are presented as given in Table 1. http://www.iasj.net/ Raghad F. ALmilly and MOHANNED H. HASAN -Available online at: www.iasj.net IJCPE Vol.18 No.2 (June 2017) 71 Table 1: Chemical Composition of adsorbent Constituent Clay Wt.% Sand Wt.% SiO2 27.90 27.03 Al2O3 7.251 0.6517 Fe2O3 6.734 0.6288 MgO 3.116 0.486 CaO 13.44 32.43 K2O 1.13 0.0516 Physical Properties The physical properties of the adsorbent was analyzed in the Oil Research and Development Center- Ministry of Oil. The tests conducted were: particle surface area, using BET method, pore volume and bulk density, according to ASTM B527. The results of surface area measurements are listed as given in Table 2. Table 2: Physical Properties of Calcined Sand- Clay Mixture Surface Area, m 2 /g Pore Volume cm 3 /g Bulk Density g/cm 3 20.33 0 .0303 0.9799 Adsorption Experiment Batch experiments were implemented to achieve the equilibrium data. Artificial wastewater was prepared from KH2PO4 at different concentrations 5, 10, 15 and 20 mg/L. Adsorbent ranging in weight 5, 10, 15 and 20 g with 10 mm in diameter were placed in individual 200 ml distilled water of 500 ml glass bottle capacity. The bottles were placed at fixed positions in a shaker. The bottles were left for a suitable time ranging from 15 min to 240 min to allow adsorption to reach equilibrium conditions. The shaker speed controller was at constant speed of 100 rpm. After shaking, the mixture was filtered through a 0.45 μm filter. Vanadate-molybdate reagent of 10 ml and 5 ml of distilled water were added to 35 ml of filtered sample. After 15 min the mixed solution was analyzed for phosphate concentration by a UV–Vis spectrophotometer at the detection wavelength of 470 nm according to [14] The adsorbed amount, qt was calculated from Equation 1 qt=(Co–Ce)V/m …(1) where qt is the amount adsorbed per unit gram of adsorbent (mg/g) in t time, Co the initial concentration (mg/L), Ce the equilibrium concentration (mg/L), V the volume of solution (200 mL), and m the weight of the adsorbent (g). The following equation was used to determine the percentage removal of phosphate at any time: 100(%)    i i C CeC R …(2) Where: Ci, Ce mg/l is the initial and equilibrium concentration of each phosphate. The shaker provided with a digital temperature sensor and speed controller. The experiments were conducted at 15, 20 and 30 °C and the shaker speed controller was at constant speed of 100 rpm. Two types of isotherm batches, were conducted, one of controlled experiments at pH 4, 7 and the other are uncontrolled experiments pH 11. Buffer solutions, 0.1M of HCl and 0.1M NaOH were added drop wise to the water to control the pH. In these runs the pH was controlled at 4, 7. Buffer solutions were not added for the runs conducted without a pH control. Results and Discussion Effect of Initial Phosphate Concentration and Contact Time The effect of the initial concentrations (5-20 mg/L) on the adsorption by (CSCM) at constant adsorbent weight, 5 g is as shown in Figure 1. A fast initial sorption capacity of phosphate at the beginning 30 min was noticed and, http://www.iasj.net/ Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent 72 IJCPE Vol.18 No.2 (June 2017) -Available online at: www.iasj.net next, the sorption capacity was further increased but with a much slower rate till it reached equilibrium in about 60 min. The equilibrium adsorption increased from 0.188 to 0.375 mg/g with increase in the initial phosphate concentration from 5-20 mg/L. Upon investigating the effect of contact time, rapid removal of P was observed in the first 30 minutes, with 89.4%, P removal in this period at 5 mg/L as shown in Figure 2. Fig. 1: Effect of initial concentration and contact time for the adsorption of phosphate on sand clay adsorbent weight=5 gm; pH 11, temperature =20 ◦C Fig. 2: Effect of initial concentration and contact time on percentage removal of phosphate contact time on percentage removal of phosphate at constant adsorbent dose 5 g and pH10-12, temperature =20 ◦C Effect of Sorbent Dosage The effect of sorbent dosage on percentage removal of phosphate is as shown in Figure 3. It was observed that the percentage removal increased from 98.9% to 100% with increase in adsorbent dose from 5 to 20 g at 5 mg/L, increase from 92% to 99% at 10 mg/L, increase from 90% to 96% at 15 mg/L, and increase from 89% to 92.7% at 20 mg/L. With a dose of 5 g (CSCM) /200 ml of simulated solution resulting in a 95%, 92%, 90%, 89% removal in P concentration at 5, 10, 15, 20 mg/L, respectively. Above this dosage of adsorbent, any increase in P removal is small. A dosing rate of 5 g was therefore recommended. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 50 100 150 200 250 300 so rp ti o n c a p a ci ty , q t( m g /g ) time (min) 5mg/l 10mg/l 15 mg/l 20 mg/l 0 20 40 60 80 100 120 0 50 100 150 200 250 300 R e m v a l % Time (min) 5 mg/l 10 mg/l 15 mg/l 20 mg/l http://www.iasj.net/ Raghad F. ALmilly and MOHANNED H. HASAN -Available online at: www.iasj.net IJCPE Vol.18 No.2 (June 2017) 73 Fig. 3: Effect of amount of adsorbent for the removal on phosphate using calcined sand clay mixture: temperature =20 ◦C, pH 11; time =60 min Effect of pH Value Experiments were conducted under varying pH between 4 and 12. The pH of the solution was adjusted with 0.1 mol/L HCl or 0.1 mol/L NaOH for only acidic and neutral solution. There is no need for controlling pH under usual case, since the adsorption process was spontaneously occurred in basic solution once the solution was added to adsorbent. The experiments were achieved at 5, 10, 15, 20 g each adsorbent dose with 5, 10, 15, 20 mg/L initial concentrations, respectively. Figure 4 removal efficiency increased from 16% to 53.4% to 98.9% when pH increased from 4 to 7 to 10 respectively. Solution pH is an important controlling parameter in determining the dominant phosphorus removal mechanism, as well as the existing ionic species in solution are responsible for a given mechanism [15]. Aqueous phosphate exists in four forms depending on the pH of a given solution. These are: 1. Phosphate ion (PO4 3- ), which predominates in strongly basic conditions; 2. Hydrogen phosphate ion (HPO4 2- ), which is the dominant form at weakly basic conditions; 3. Dihydrogen phosphate ion (H2PO4 - ), which predominates in weakly acidic conditions; and 4. Trihydrogen phosphate (H3PO4) which is the main form at strongly acidic conditions. (PKa=2.2) …(3) (PKa=7.2) …(4) (PKa=12.3) …(5) The logarithmic constant, pKa, is given as …(6) A smaller pKa value (i.e., a larger Ka value). A strong acid does not change pH and is therefore vital to understanding the possible removal mechanisms associated with phosphate. In sorption studies involving the uptake of phosphorus on to calcined sand-clay mixture (CSCM), it was found that the highest phosphorus removal occurred at pH 10-12. There was three different forms of phosphate, e.g., , 88 90 92 94 96 98 100 102 0 5 10 15 20 25 R e m o v a l % Adsorbent dose (gm) 5mg/l 10mg/l 15mg/l 20mg/l http://www.iasj.net/ Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent 74 IJCPE Vol.18 No.2 (June 2017) -Available online at: www.iasj.net and in the solution as described in Equations 3-5. Generally, governing species in the PH region between 4 and 10, and with notice that species were governed in slightly alkaline conditions, but species governed in slightly acidic conditions. dominated over species between pH 10- pH 12, while species governed at pH higher than 12.5, [16]. There are several factors that controls the phosphate adsorption: Phosphate speciation in solution, pHZPC (zero point charge) of the adsorbent and the affinity of phosphate ions towards the adsorbent [17]. The pH at which the net surface charge zero on the adsorbent is called pHZPC. The surface charge of the adsorbent become negative when pH is less than pHZPC value, therefor a higher repulsion between the binding sites and phosphate ions resulting lower phosphate uptake, while the surface become a net positive charge when the pH is greater than pHZPC that improve coulombic attraction between the sites and the phosphate ions leading an increase in phosphate adsorption. The solution begins to donate more protons than hydroxide groups, When the pH is less than PKa, that cause the sorbent surface positively charged attracting negatively charged species [18]. In this study, the higher removal of phosphates at pH 10-12 (less than pka value of 12.3) indicates that the species involved in adsorption were affected by pH. Maximum phosphate sorption took place when it was higher than PHZPC of the (CSCM) surface, and less pka value 12.3 of , the conditions that facilitated (CSCM) surface to be positively charged. This observations have revealed that was the key species involved in range of adsorption process. The phenomenon may be explained another mechanism via precipitation. Hydrolysis of metal oxides generate metal cation and hydroxyl anion ( ) as the following equation. …(7) ( ) …(8) Fig. 4: Effect of pH value on the phosphate removal efficiency at different concentration, Dose = 5 g and equilibrium time of 60 min 0 20 40 60 80 100 120 PH4 PH7 PH12 5 gm 10 gm 15 gm 20 gm % R e m o v a l http://www.iasj.net/ Raghad F. ALmilly and MOHANNED H. HASAN -Available online at: www.iasj.net IJCPE Vol.18 No.2 (June 2017) 75 The cationic species participate in phosphate up taking through electrostatic interaction, while the anionic species used inner sphere ligand exchange mechanism. Likewise phosphate metal precipitation took place as the equation given below [19]: …(9) The presence of calcium oxides and silicates oxides in relatively large quantities as shown in Table 2.1 may support the precipitation mechanism. Thus phosphorus-removal pathway in the (CSCM ) surface are adsorption on to the (CSCM) surface by precipitation of metallic phosphate salts. The orthophosphates which is particularly form of phosphorus, was indicated that able to absorbed by clay minerals and various organic soils fraction in the soil matrix and chemically precipitate with Ca (at neutral to alkaline pH values) [20]. Effect of Temperature The effect of temperature on the phosphate adsorption rate (qe) was also examined over temperature range of 15- 30 °C. Figure 5 shows the effect of temperature on the adsorption rate. It can be seen that the phosphate adsorption rate on calcined sand-clay mixture (CSCM) decreases with increasing temperature from 15 to 30 °C. The maximum adsorption rate was 0.63 mg/g at 15 °C decreased to 0.47 mg/g at 30 °C. This means that the adsorption of phosphate ions was improved at lower temperatures. The sorption of phosphate is exothermic. A similar observation was reported for removal of phosphate using dolomite mineral [21]. Thus the amount of adsorption decreased with increasing temperature. In contrast, the sorption of phosphate was endothermic used alginate-calcium carbonate composite beads [22]. It is noticed that removal efficiency decreased from 95% to 79%, 89% to 70%, 78% to 66%, 75% to 60% when temperature raised from 15 °C to 30 °C, at varying concentrations 5, 10, 15, 20 mg/l, respectively. As shown in Figure 6. Fig. 5: Effect Of the temperature on the sorption capacity pH=10-12; amount adsorbent=5 gm; contact time =30 min; at different concentrations 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 285 290 295 300 305 so rp ti o n c a p a si ty m g /g Temperature K http://www.iasj.net/ Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent 76 IJCPE Vol.18 No.2 (June 2017) -Available online at: www.iasj.net Fig. 6: Effect Of the temperature on the phosphate removal pH=10-12; amount adsorbent=5 gm; contact time =30 min; at different concentrations Isotherm Equations for Single- Solute Adsorption Two-Parameter Isotherms The well-known equations proposed by Langmuir (1918) and Freundlich (1906) are typical representatives of the group of two-parameter isotherms. They belong to the most frequently used isotherm equations. The Langmuir isotherm has the form: …(10) A linear regression is also possible because all two-parameter equations can be linearized. For Langmuir isotherm, different types of linearization are possible as follows: = …(11) The Langmuir equation is valid for monolayer sorption onto the surface and energetic homogeneity of the adsorption sites. On the other hand, the Langmuir isotherm equation was also found to be applicable in cases where the underlying assumptions obviously not fulfilled. and b are Langmuir parameters related to maximum adsorption capacity (mg of solute per g of adsorbent) and free energy of adsorption, respectively. is the concentration of solute at equilibrium (mg/l) and is the amount of solute adsorbed per unit weight of adsorbent at equilibrium (mg of adsorbate per g of adsorbent). It is possible to estimate and b from both intercept and slope, respectively through linear plot of the experimental data of versus as illustrated in Figure 7 and tabulated in Table 3. The higher values of the correlation coefficient ( ) for both isotherms indicates that obviously best fit to experimental data. It is possible to explain good fitness in terms of surface nature of the adsorbent and affinities to towards phosphate concerning of various mineralogical forms exist in the adsorbent. The Freundlich isotherm is given by: …(12) Where K and n are the isotherm parameters. The Freundlich isotherm can describe neither the linear range at very low concentrations nor the saturation effect at very high concentrations. By contrast, the medium concentration range is often 0 10 20 30 40 50 60 70 80 90 100 285 290 295 300 305 R e m o v a l % Temperature K 5 mg/l 10 mg/l 15mg/l 20mg/l http://www.iasj.net/ Raghad F. ALmilly and MOHANNED H. HASAN -Available online at: www.iasj.net IJCPE Vol.18 No.2 (June 2017) 77 very well represented. Freundlich isotherm is a common used to describe the characterization of adsorption from aqueous solutions. It has been applied for the prediction of multi solute adsorption, the equilibrium relationship in the most kinetic and breakthrough curve models. It is convenient to convert Freundlich isotherm into the logarithmic form as: …(13) Where K describe the strength of adsorption. High K value means high the adsorbent loading. The exponent n value indicate the degree of isotherm curvature as well as the energetic heterogeneity of the adsorbent surface. The isotherm becomes the more concave when the lower the n value is. If the concentration has a value of 1 in the respective unit, the loading equals the value of K. In experiments the exponent n is possible take any value. In practice, however, mostly n values lower than 1 are found. With n = 1, the isotherm becomes linear. Freundlich isotherms are characterized as favorable with n < 1 that display relative high adsorbent loadings at low concentrations, whereas are recognized as unfavorable with n > 1. The value of K and n that represent intercept and slope, respectively be estimated from the linearization equation of 13 through taking logarithm of both sides equation 12 as illustrated in Figure 8 and tabulated in Table 3 .As shown in Figures 7-8 the ( ) value for Langmuir model (0.9975) is slightly higher than of the Freundlich model (0.9821) which may denote the control of monolayer adsorption process over intra-molecular interactions among the adsorbed phosphate [19]. From both figures it can be seen that Langmuir model showed a better fit of the data than the Freundlich model. Fig. 7: Langmuir adsorption isotherm for phosphate on calcined sand clay mixture: temperature=20 ◦C; pH 10-12; adsorbent dose =5 gm; time =30 min Table 3: Isotherm constants for phosphate adsorption onto sand clay mixture Parameters Temperature, °C 15 20 30 Langmuir qm mg/g 0.616 0.67 0.631 b (L/mg) 1.85 .678 0.312 R 2 0.9908 .9978 0.9907 Freundlich n 2.73 2.099 1.8 kf(mgL -1/n g -1 L 1/n ) 0.344 0.25 0.157 R 2 0.9771 0.9821 0.995 y = 2.201x + 1.4888 R² = 0.9975 0 1 2 3 4 5 6 7 0 0.5 1 1.5 2 2.5 1 /q e 1/ce http://www.iasj.net/ Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent 78 IJCPE Vol.18 No.2 (June 2017) -Available online at: www.iasj.net Fig. 8: Freundlich adsorption isotherm for phosphate on calcined sand clay mixture: temperature =20 ◦C; pH 10-12; adsorbent dose =5 gm; time =30 min The mathematical expression of Langmuir isotherm of dimensionless constant which is commonly known as separation factor (RL) can be defined as equation 14: …(14) In this regard RL value can be considered as a preferential indicator of the adsorption. In deeper clarification, there are four values of the RL, for favorable adsorption (0 < RL <1), for unfavorable (RL > 1), for irreversible (RL = 0) and for linear (RL = 1). Values of RL were proved that calcined sand clay mixture is favorable for adsorption of phosphate under conditions studied as shown in Table 5 where the values of RL were in the range of 0-1at all temperatures studied. Table 4: The maximum adsorption capacity of phosphate on different adsorbents Adsorbent material qm mg/g References Modified bentonite 34.48 TANG yan-Kui et al., 2006 Burned kaolin 0.61 Majd I.Abdul Wahab et al., 2011 Calcined sand clay mixture 0.63 The present work Table 5. The parameter RL indicates the shape of isotherm as function of temperature. Temperature 15, °C Nominal Concentration mg/l Actual Concentration mg/l RL 5 5.18 0.094 10 11.65 0.044 15 16.6 0.0315 20 21 0.025 Temperature 20, °C 4.76 0.236 11.61 0.112 16.56 0.081 20.88 0.065 Temperature 30, °C 5.1 0.385 10.66 0.231 15.33 0.172 19.9 0.138 Thermodynamic of Phosphate Adsorption onto Calcined Sand Clay Mixture (CSCM) The thermodynamic factors of phosphate adsorption onto sand-clay mixture including changes in standard enthalpy (ΔH°), standard entropy (ΔS°) were estimated by using the following Van’t Hoff equation [21], …(15) The Gibbs free energy (ΔG°) was evaluated by using equation 16: y = 0.4764x - 0.599 R² = 0.9821 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Lo g q e Log ce http://www.iasj.net/ Raghad F. ALmilly and MOHANNED H. HASAN -Available online at: www.iasj.net IJCPE Vol.18 No.2 (June 2017) 79 ΔG°=-RTlnK …(16) where R is gas constant (8.314 J.mol- 1.K-1), K is the equilibrium constant at temperature T can be calculated from the ratio of amount adsorbed on solid at equilibrium Ci and the equilibrium concentration of phosphate Ce (mg/L) as expression: K = Ci/Ce. The negative values of  G were (- 2.63, -2.06, -1.021 kJ/mol) at 288, 293, 303 k, respectively as shown in Table 6 which indicate spontaneous process by (CSCM) as an adsorbent. Values of  H and  S were calculated from the slope and intercept of the Van’t Hoff linear plot of log K versus 1/T as shown in Figure 9. The negative values of  H (-33.8 kJ/mol) as shown in Table 5 prove the exothermic nature of adsorption. The negative values of  S (-108.25 J/mol.K) reflect lower randomness at the solid/solution interface during the adsorption of phosphate. Thermodynamic factors were reported  H (-5.85 kJ/mol),  S (-10.17 J/mol.K) for the adsorption of phosphate on dolomite [21]. Fig. 9: Vant’t Hoff plot for the adsorption of phosphate onto calcined sand clay mixture adsorbent (pH=10-12) Table 6: Thermodynamic parameters for the adsorption of at various temperatures onto calcined sand clay mixture Temp. (ºC) kJ/mol kJ/mol J/mol.k 15 3 -2.63 -33.8 -108.25 20 2.33 -2.06 30 1.5 -1.021 Conclusions The results of the present work can provide a process for developing a low-cost technology based on adsorption by calcined sand-clay mixture for phosphate removal from wastewater. The following points can be concluded from the present study: calcined sand-clay mixture (CSCM) removes phosphate from aqueous solution rapidly. Phosphate may be removed by adsorption and/or by precipitation of calcium phosphate. Phosphate adsorption by (CSCM) increased with the increase in pH and reached spontaneously at the maximum adsorption in the pH range of 10-12. As the initial concentration of phosphate increases 5 to 20 mg/l, the amount of adsorbed phosphate on y = 1766.4x - 5.6539 R² = 0.9998 0 0.1 0.2 0.3 0.4 0.5 0.6 0.00325 0.0033 0.00335 0.0034 0.00345 0.0035 Lo g K c 1/T k-1 logKc 3 4 PO  G H  S http://www.iasj.net/ Waste Water Treatment by Liquid-Solid Adsorption Using Calcined Sand-Clay Mixture Adsorbent 80 IJCPE Vol.18 No.2 (June 2017) -Available online at: www.iasj.net the adsorbent increases. As the temperature increases 15-30 ◦C the adsorption rate decreases over the studied adsorbent which indicates that the adsorption of phosphate was favoured at lower temperature, since the adsorption of phosphate is exothermic. Equilibrium isotherm adsorption data obey both Langmuir and freundlich models with slightly fit by Langmuir. The maximum adsorption capacity of (CSCM) is 0.835 mg/g P. (CSCM) can be used as an effective, low-cost, available and locally adsorbent for the removal of phosphate. Nomenclature b Langmuir isotherm constant L/mg CSCM Calcined sand clay mixture C Concentration of adsorbate in feed mg/L Ce Equilibrium phosphate concentration mg/L Co Initial concentration of phosphate ions mg/L Cf Final concentration of phosphate ions mg/L Kf Freundlich isotherm constant mgL-1/ng-1L1/n n Freundlich intensity parameter qm The maximum amount of adsorbate per unit weight of adsorbent mg/g qe Concentration of adsorbate in solid phase at equilibrium mg/g qt Concentration of adsorbate in solid phase at time t mg/g RL Separation factor R 2 coefficient of determination rpm rotation per minute References 1. De-Bashan L. E., Y. Bashan, 2004, “Recent advances in removing phosphorus from wastewater and its future use as fertilizer”, Water Res. 38, 4222–4246. 2. Tran N., P. Drogui, J.F. Blais, G. 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