Abstract

This work concerns the elimination of the organic pollutant; Bemacid Red (BR), a rather persistent dye present in wastewater from the textile industry in western Algeria, by adsorption on carbon from an agricultural waste in the optimal conditions of the adsorption process. An active carbon was synthesized by treating an agro-alimentary waste, the date stones that are very abundant in Algeria, physically and chemically. Sample after activation (SAA) with phosphoric acid was highly efficient for the removal of BR. The characterization of this porous material has shown a specific surface area that exceeds 900 m2/g with the presence of mesopores. The iodine value also indicates that the activated carbon obtained has a large micro porosity. The reduction of the infrared spectroscopy (FTIR) bands reveals that the waste has been synthesized and activated in good conditions. Parameters influencing the adsorption process have been studied and optimized, such as contact time, adsorbent mass, solution pH, initial dye concentration and temperature. The results show that for a contact time of 60 min, a mass of 0.5 g and at room temperature, the adsorption rate of the BR by the SAA is at its maximum. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were studied to analyse adsorption kinetics. The result shows the adsorption kinetic is best with the pseudo-second-order model. In this study, Langmuir, Freundlich and Temkin isotherms were investigated for adsorption of BR onto SAA. The Freundlich and Temkin isotherms have the highest correlations coefficients. The suggested adsorption process involves multilayer adsorption with the creation of chemical bonds. The mechanism of adsorption of BR by SAA is spontaneous and exothermic, and the Gibbs free energy values confirm that the elimination of the textile dye follows a physisorption.

INTRODUCTION

Dyes from textile, leather, cosmetics, paper, dye synthesis, food processing, pharmaceuticals and plastics industries are the important source of environmental contamination (Yao et al. 2010).

Various methods have been studied to remove dyes from wastewaters, including chemical oxidation (Liu et al. 2011), biodegradation (Ong et al. 2005), electrocoagulation (Golder et al. 2005) and adsorption (Vargas et al. 2011). However, these methods have many disadvantages, as they require expensive equipment and/or a continuous need for chemicals (Malkoc et al. 2006). Moreover, sometimes the above-mentioned methods fail to meet the Environmental Protection Agency requirements (Borba et al. 2008; Baccar et al. 2009). Activated carbon is one of the most widely used adsorbents due to its high adsorbent power, but its cost and its regeneration are very expensive (Sudhakar et al. 2016). Appropriate agro-food waste (lignocellulosic), such as fishing and date cores, rice, pistachio and almond shells, have been studied in recent years as active carbon precursors and receive special attention (Baccar et al. 2009). The objective of this study is to develop an inexpensive adsorbent from date stones and explore the possibility of using it to remove the dangerous dye Bemacid Red C24H20ClN4NaO6S2 present in a wastewater by adsorption.

METHODS

Preparation of activated carbon

The amount of date stones was washed initially with hot water to remove impurities, dust, and water-soluble substances (Namane et al. 2005), and in a second step, distilled water was used to remove dirt and other contaminants and the stones were oven dried at 110 °C for 24 hours. Then, the sample was dried in an oven at about 200 °C for 3 hours. Finally, the stones were crushed and stored (SBA) before activation.

50 g of natural date stones were added to the aqueous solution of phosphoric acid (1/1) and stirred with heating to 100 °C for 1 hour. The sample was filtered and dried in an oven at 100 °C for 24 hours. Thereafter, the resulting sample was carbonized at a heating rate of 10 °C/min to 600 °C for 3 hours in a muffle furnace (NaberTherm B180). After cooling, the carbonized sample was washed with an aqueous solution of hydrochloric acid (10% by weight) (Papirer et al. 1995) in order to remove the excess dehydrating agent and the soluble ash fraction, and then distilled water to remove residual organic and mineral matter. Washing with water easily removes most of the residues from activating agents (Namane et al. 2005). The sample was washed until the filtrate reached a neutral pH. The resulting sample was dried in an oven at 100 °C for 24 hours (SAA).

Characterization of the prepared adsorbent

Zero point charge pH (pHzpc)

The zero charge point (pHzpc) of the material was determined by the electrochemical method cited by Altenor (Altenor et al. 2009). A series of experiments was established by stirring 1 g of SAA in several solutions of distilled water at different pHs ranging from 2 to 12. The final pH was measured after 24 hours of stirring.

Iodine adsorption capacity

The iodine adsorption capacity of activated carbon prepared from date pits (SAA) was determined (Dhidan 2012).

10 mL of 0.01 N iodine solution was titrated with a 0.1 N sodium thiosulfate solution in the presence of a starch solution as an indicator until it became colourless. The reading volume corresponds to Vb.

0.05 g of SAA was mixed with 15 mL of an aqueous solution of iodine (0.1 N) and stirred vigorously for 5 min. The mixture was titrated with a standard sodium thiosulfate solution using a starch solution as an indicator, keeping the burette reading corresponding to Vs. The iodine number was then calculated by using the following equation: 
formula
(1)
  • I.N: iodine number (mg.g−1)

  • Vb and VS: volume of sodium thiosulfate solution required for blank and sample titrations respectively (mL).

  • N: normality of sodium thiosulfate solution (mol.L−1)

  • 126.9: atomic weight of iodine (g.mol−1).

  • M: mass of SAA used (g).

Ash content

The ash content was determined by standard method (CEFIC 1986). 0.5 g of activated carbon, with an average particle size of 250 µm, was dried at 80 °C for 24 h and placed in previously weighed ceramic crucibles. The samples were heated in a muffle furnace at 650 °C for 3 h. The crucibles were then cooled to room temperature and weighed. The ashing rate was calculated using the following equation: 
formula
(2)
where:
  • Wm1: weight of the original sample used (g);

  • Wm2: weight of crucible containing a dried sample (g);

  • Wm3: weight of crucible containing an original sample (g).

Moisture content

The moisture content was determined using the oven drying method (Adekola & Adegoke 2005). 0.5 g of activated carbon was placed in a previously weighed ceramic crucible. The sample was dried at 110 °C until the weight was stable. Thereafter, the sample was cooled to room temperature and weighed. The moisture content was calculated using the following equation: 
formula
(3)

Surface area (SBET)

The specific surface area of the SAA was evaluated by adsorption of N2 at 77 K, using an ASAP 2010 V5.0. The BET model (Brunauer, Emmett and Teller) was applied. It consists of studying the nitrogen adsorption isotherm and evaluating the surface area (SBET) of the sorbent.

FTIR analysis

The surface functional groups were studied by Fourier transform infrared spectroscopy (FTIR Perkin Elmer Universal ATR Sampling Accessory). The FTIR spectra of the raw material and the resulting activated carbon were recorded between 650 and 4,000 cm−1 in a Perkin Elmer spectrometer.

Adsorbate

Bemacid Red C24H20ClN4NaO6S2, (M = 583 g.mol−1) is an industrial synthetic dye intended for the dyeing of chemical textiles of polyamide nature and which was supplied to us by a textile dyeing company in western Algeria. Bemacid Red (BR) belongs to group E, which is characterized by a high level of lightfastness, good migration power, good combinability, fast exhaustion even at low temperatures and rapid fixation with saturated steam. Bemacid Red is soluble in water and was used directly in the experiment without pre-treatment.

Adsorption study

A solution of 0.05 g.L−1 BR was prepared by dissolving an appropriate amount of dye, which was diluted to the required concentration. Various parameters that influence the adsorption process have been optimized. The optimal contact time was determined by stirring 1 g of SAA with 50 ml of a solution of BR 0.05 g.L−1 at pH = 6 at times ranging from 5 to 90 min. The effect of the adsorbent dose was investigated by varying the amount of SAA from 0.1 to 0.6 g in 50 ml of 0.05 g.L−1 of dye solution at pH = 6. 0.5 g of SAA was mixed with 50 ml of BR solution 0.05 g.L−1 at different pH values between 2 and 12 (the pH of the solution was adjusted using NaOH and HCl 0.1N) in order to study the effect of pH. To study the effect of the initial concentration of the BR dye, a mass of 0.5 g of SAA was mixed with 50 ml of the dye solution at different concentrations (0.01 to 0.07 g.L−1). The effect of temperature on the adsorption phenomenon was studied by varying the temperature from 8 to 55 °C, maintaining the dye concentration at 0.05 g.L−1, the time at 60 min, the mass of the adsorbent at 0.5 g and the pH of the solution at 2.

The dye concentration in the supernatant solution was determined at the characteristic wavelength BR λmax = 500 nm; by UV–visible spectrophotometer (Perkin Elmer UV-vis Lambda 45).

The percentage removal of the dye and the amount of dye adsorbed on the adsorbents (qe) was calculated using Equations (4) and (5), respectively: 
formula
(4)
 
formula
(5)
where:
  • qe: amount of dye adsorbed on adsorbent at equilibrium (mg.g−1);

  • C0: initial equilibrium concentration of dye in solution (mg.L−1);

  • Ce: equilibrium concentration of dye in solution (mg.L−1);

  • V: volume of the solution (L);

  • m: mass of adsorbent (g).

Kinetics studies

Pseudo-first-order Equation (6), pseudo-second-order Equation (7) and intraparticle diffusion model Equation (8) were tested (McKay 1984; Ho & McKay 2000; Li et al. 2009). 
formula
(6)
 
formula
(7)
 
formula
(8)
where:
  • qe and qt: adsorption capacity of the adsorbate (mg.g−1) at equilibrium and at time t (min);

  • k1 and k2: pseudo-first-order and pseudo-second-order rate constant;

  • ki: intraparticle diffusion rate constant;

  • C: the intercept.

Studies of adsorption isotherms models

The adsorbed amount of BR on SAA as a function of equilibrium concentration was determined as mixed 0.5 g of SAA with 50 ml of BR solution with various initial concentrations of 10, 20, 30, 40, 50, 60 and 70 mg.L−1 for 60 min, at pH = 2 and room temperature.

To determine the maximum BR capacity of SAA, the equilibrium isotherm data were correlated by the Langmuir (Clarke & Irving Langmuir 1916), Freundlich (Freundlich 1906; Haghseresht & Lu 1998), and Temkin (Sudhakar et al. 2016) isotherms. These equations can be written as Equations (9)–(11): 
formula
(9)
 
formula
(10)
 
formula
(11)
where:
  • qm : saturated adsorption capacity of the adsorbate (mg.g−1);

  • KL: constant of Langmuir isotherm (L.mg−1);

  • KF and n: parameters of the Freundlich isotherm;

  • KT: Temkin constant (L.mol−1);

  • ΔQ: variation of adsorption energy (J.mol−1).

Thermodynamic parameters

Gibbs free energy ΔG° (kJ.mol−1), standard enthalpy ΔH° (kJ.mol−1) and standard entropy ΔS° (J.mol−1.K−1) could provide information about the mechanism of adsorption and were determined using the van 't Hoff equation: 
formula
(12)
 
formula
(13)
 
formula
(14)
where:
  • R: universal gas constant (8.314 J.mol−1.K−1);

  • T: absolute temperature (K);

  • Kd: thermodynamic distribution coefficient.

RESULTS AND DISCUSSION

Characterization of adsorbent

The adsorption isotherm (Figure 1) is divided into two parts: the first part (AB) has a slow increase of the convex curve and a large increase in the second part (BC) due to the multilayer adsorption, the filling, and the capillary condensation. In this case, no adsorption saturation point exists on the curve (Wang et al. 2012).

Figure 1

N2 adsorption-desorption isotherm of SAA.

Figure 1

N2 adsorption-desorption isotherm of SAA.

The shape of the curve shows a type IV adsorption-desorption isotherm according to the BDDT classification (Brunauer et al. 1940) with the presence of H3 hysteresis of the International Union of Pure and Applied Chemistry (IUPAC), which confirms the presence of mesopores (Song et al. 2009) in the form of a slit (Wang et al. 2012).

Hysteresis appeared at high relative pressure (p/p° > 0.6), suggesting that the synthesized material has a heterogeneous distribution of porous size (Li et al. 2007).

The results obtained show that the SAA has a surface area equal to 942 m2.g−1, a pore volume of 0.504 cm3/g and an average pore size of 2.14 nm. The average pore diameter of 2.14 nm indicates that the SAA is a mesoporous adsorbent according to the IUPAC classification.

Chemically activated carbon with H3PO4 shows a low pHzpc value (2.59) (Figure 2), which indicates a high acidic group content (Altenor et al. 2009). The acidic or basic character of a surface is expressed by its isoelectric point. If the pH of the solution is basic, the surface is acidic and vice versa.

Figure 2

Zero point charge pH (pHzpc).

Figure 2

Zero point charge pH (pHzpc).

If pH < pHzpc then the net charge is positive

If pH > pHzpc then the net charge is negative

As the pH of the solution decreases to pHzpc, the density of positive ions on the surface increases, causing strong attraction with BR that is negatively charged.

Main chemical and textural properties of the activated carbons are listed in Table 1. In addition, the pore characteristics such as surface area, total pore volume, and pore size of SAA at best conditions are 942 m2.g−1, 0.504 cm3.g−1, and 2.14 nm respectively. These values confirm the well-developed pore structure of SAA compared to 1,080.11 m2.g−1, 0.622 cm3.g−1 and 2.850 nm for commercial activated carbon (CAC), respectively. The iodine number of SAA (1,142 mg.g−1) is higher than that obtained by Haimour and Emeish (Haimour & Emeish 2006). It should be emphasized that the optimum adsorption capacity of SAA iodine is slightly higher than that of a CAC, which has an iodine adsorption value of 1,000 mg.g−1 (Song et al. 2013). The contents of moisture and ash were 5.6 and 2.09% respectively. According to the results, the low ash content indicates that the precursor can withstand high-temperature treatment during carbonization and chemical activation (Garba & Rahim 2016).

Table 1

Chemical and textural properties of SAA

Characteristics Values 
Surface area (m2.g−1942 
Pore volume (cm3.g−10.504 
Pore size (nm) 2.14 
pHzpc 2.59 
Iodine number (mg.g−11,142 
Ash content (%) 2.09 
Moisture content (%) 5.6 
Characteristics Values 
Surface area (m2.g−1942 
Pore volume (cm3.g−10.504 
Pore size (nm) 2.14 
pHzpc 2.59 
Iodine number (mg.g−11,142 
Ash content (%) 2.09 
Moisture content (%) 5.6 

Figure 3 shows the FTIR spectrum of the SBA (sample before activation) and SAA. The strong peaks, which appear at 3,685.8, 3,473.7 and 3,368.33 cm−1, are attributed to bonded O-H groups (alcohols, phenols, and carboxylic acids) (Belala et al. 2011; Abbas & Ahmed 2016; El Messaoudi et al. 2016). The peaks between 2,989 cm−1 and 2,853 cm−1 correspond to the C-H (alkanes) (Abbas & Ahmed 2016; El Messaoudi et al. 2016). The peak at 1,744.08 cm−1 is characteristic of the stretching vibration of C = O of the carboxylic acids of xylan present in hemicelluloses (Sun et al. 2005; Pavan et al. 2008; El Messaoudi et al. 2016). Bands at 1,564.5 and 1,456.6 cm−1 attributed to the deformation C = C (aromatic of lignin) (Bouchelta et al. 2008; El Messaoudi et al. 2016). The vibration at 1,394.38, 1,376.4, 1,240.4 and 1,228.3 cm−1 attributed to the C-O methoxy groups of lignin (Al-ghouti et al. 2013; El Messaoudi et al. 2016). The band at 1,148.3 cm−1 corresponds to C-O (alcohols, carboxylic acids, ester, ethers) (Abbas & Ahmed 2016; El Messaoudi et al. 2016). Bands at around 1,064 cm−1 are attributed to the S-O elongation vibration (Kyzas et al. 2015; El Messaoudi et al. 2016). The peaks between 1,010 cm−1 and 936 cm−1 correspond to C-O-C bonds of cellulose (Sain & Panthapulakkal 2006; Al-ghouti et al. 2010; El Messaoudi et al. 2016). Peaks at 870,54 cm−1 and 880,1 cm−1 correspond to C-H deformation in cellulose (Sain & Panthapulakkal 2006; Al-ghouti et al. 2010; El Messaoudi et al. 2016). The band at 720,19 cm−1 is attributed to the C-X (alkyl halide) (Abbas & Ahmed 2016). The main groups present in the date stones before activation are the carbonyl and hydroxyl groups also found in the cellulosic biomass (Abbas & Ahmed 2016). Comparing the two FTIR spectra of SAA and SBA, we found that after activation various functions disappeared, such that: O-H, C = O, C-O-C, C-X.

Figure 3

FTIR spectra of SBA and SAA.

Figure 3

FTIR spectra of SBA and SAA.

Effect of contact time

Figure 4 shows a rapid increase in the elimination of the Bemacid Red with increasing contact time. Discoloration of the solution was observed from the first contact time (5 min). After a sufficient time of 60 minutes, the residual concentration of the red dye in the aqueous phase reaches its limit.

Figure 4

Effect of contact time.

Figure 4

Effect of contact time.

The removal of BR (0.05 g.L−1) is very fast at first contact, due to the availability of active sites. The adsorption rate becomes stable after 60 minutes of stirring and reaches equilibrium (Papirer et al. 1995). This equilibrium is due to the saturation of the majority of sites by dye ions.

Effect of adsorbent amount

The effect of the adsorbent dose is investigated by varying the amount of SAA from 0.1 to 0.6 g in 50 mL of 0.05 g.L−1 of BR dye solution. Figure 5 shows that with an increase in mass, the rate of BR adsorption increases from 25 to 95%. This is due to the presence of more active sites on the surface (Papirer et al. 1995; Kyzas et al. 2015). The initial increase in adsorption is due to the availability of a larger surface area of the adsorbent, but a further increase in the amount saturates the surface of the adsorbent and the equilibrium state is reached. The adsorption efficiency is reduced following the aggregation of the adsorption sites by an excess of adsorbent.

Figure 5

Effect of adsorbent dose.

Figure 5

Effect of adsorbent dose.

Effect of pH

0.5 g of SAA was mixed with 50 mL of BR solution at different pH values between 2 and 12 (the pH of the solution was adjusted using sodium hydroxide and nitric acid). Figure 6 shows the effect of the solution pH on the adsorption capacity of the SAA and it was found that the amount of adsorbed BR per unit of activated carbon increased significantly at a low pH.

Figure 6

Effect of pH.

Figure 6

Effect of pH.

SAA showed significant variation in percent removal from 99 to 66% on changing pH from 2 to 12. Maximum removal of SAA in an acidic medium may be due to the carboxylic and phenolic groups (cellulosic compounds) present on the adsorbent surface (Ferrero 2007). At low pH, the adsorption is at its maximum (at strongly acidic pH); this confirms the result obtained for the pHzpc. At pH < pHzpc, the surface is positively charged, which produces an attraction with the negatively charged pollutant.

Effect of initial concentration

Figure 7 shows that the adsorption rate was very fast at the first contact time and then gradually increased with time until the adsorption reached equilibrium. This rate of kinetics is due to the adsorption of the dye on the outer surface of the adsorbent at the beginning of the process. When the adsorption on the outer surface reaches saturation, the dye diffuses into the pores of the adsorbent (adsorption on the inner surface of the adsorbent) (Kushwaha et al. 2014). The amount of BR adsorbed on SAA increased with increasing initial concentration. The initial concentration provides a driving force for overcoming the mass transfer resistance of dye molecules between the liquid and solid phases during adsorption (Ghaedi et al. 2014). This phenomenon can be explained by the fact that the initial high concentration of the dye provides a higher concentration gradient between the liquid phase and the solid phase, which increases the adsorption capacity (Maneerung et al. 2016).

Figure 7

Effect of initial concentration.

Figure 7

Effect of initial concentration.

Effect of temperature

The effect of temperature on the adsorption phenomenon was studied by varying the temperature of the reaction medium from 8 to 55 °C (Figure 8).

Figure 8

Effect of temperature.

Figure 8

Effect of temperature.

In the early stages, the percentages of elimination are almost identical for low temperatures. Beyond 5 minutes of stirring, this rate differs and the percentage of elimination reaches 90% for 35 °C, 85% for 8 °C and 25 °C and 70% for 55 °C. However, from 60 min, the adsorption rates increase for all temperatures and reach the same rate of elimination, which is 95%. Following these findings, it is best to work at room temperature.

Kinetic study

The value of the correlation coefficient R2 (Table 2) of the pseudo-second-order kinetic model, which is close to 1.0, and the value of the amount of equilibrium adsorbed dye (qe), which is very close to that of the experimental value (1,320.25 mg.g−1), indicate that the adsorption kinetics follow the pseudo-second-order model.

Table 2

Kinetic parameters for adsorption of BR on SAA

Kinetic models Constants Results
 
Ci=30 mg.L1 Ci=50 mg.L1 Ci=70 mg.L1 
Pseudo first order qe,cal (mg.g−11758,11 1805,99 1956,23 
k1 (mn−17,28.10−3 9,86.10−3 11,23.10−3 
R2 0.92 0,9378 0,68 
Pseudo second order qe,cal (mg.g−11270,33 1280,39 1300,54 
k2 (mn−11,63.10−3 2,53.10−3 2,48.10−3 
R2 0.99 0,9999 0,987 
Intraparticle diffusion qe (mg.g−11308,11 1511,03 1,450 
2,12 2,44 2,98 
ki 1,12 1,25 1,32 
R2 0,9321 0,9308 0,926 
Kinetic models Constants Results
 
Ci=30 mg.L1 Ci=50 mg.L1 Ci=70 mg.L1 
Pseudo first order qe,cal (mg.g−11758,11 1805,99 1956,23 
k1 (mn−17,28.10−3 9,86.10−3 11,23.10−3 
R2 0.92 0,9378 0,68 
Pseudo second order qe,cal (mg.g−11270,33 1280,39 1300,54 
k2 (mn−11,63.10−3 2,53.10−3 2,48.10−3 
R2 0.99 0,9999 0,987 
Intraparticle diffusion qe (mg.g−11308,11 1511,03 1,450 
2,12 2,44 2,98 
ki 1,12 1,25 1,32 
R2 0,9321 0,9308 0,926 

On the other hand, for the intraparticle diffusion model, the low value of R2 for the linear plot of qt versus t1/2 indicates that this model could not properly fit the experimental kinetic data.

Adsorption isotherm study

From the values of the correlation coefficient (R2) presented in Table 3, the BR adsorption process on SAA follows the Freundlich and Temkin models. The high value of n (>1) indicates a favorable adsorption. The constant n denotes the interaction between the exchange sites in the adsorbent and the BR ions. The Temkin model indicates that the adsorption mechanism between the dye and the sorbent is chemical, so the adsorption occurs at the most energetic sites in the beginning (Abdel-Ghani et al. 2007; Tiwari et al. 2015).

Table 3

R2 and constants values for the different isotherm models

Models Constants values 
Freundlich 
 R2 0.9904 
 1/n 0.211 
 KF (mg.g−1)(L.mg−1)1/n 3.476 
Langmuir 
 R2 0,86 
 qm (mg.g−15.017 
 KL (L.mg−11.0395 
Temkin 
 R2 0,973 
 BT (kJ.mol−124.03 
 KT (L.mol−12.35 
 ΔQ (J.mol−11,930 
Models Constants values 
Freundlich 
 R2 0.9904 
 1/n 0.211 
 KF (mg.g−1)(L.mg−1)1/n 3.476 
Langmuir 
 R2 0,86 
 qm (mg.g−15.017 
 KL (L.mg−11.0395 
Temkin 
 R2 0,973 
 BT (kJ.mol−124.03 
 KT (L.mol−12.35 
 ΔQ (J.mol−11,930 

Thermodynamic study

The effect of temperature on adsorption capacities was studied by performing a series of experiments at 281, 298, 308 and 328 K. Thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°) and Gibbs free energy (ΔG°) were determined by Equations (7) and (8). The calculated values are given in Table 4. The decrease in ΔG° values with increasing temperatures indicates that adsorption becomes less favorable at higher temperatures. Negative values of ΔG° indicate that the adsorption process is spontaneous. The negative value of ΔH ° suggests that the BR adsorption process on SAA is exothermic (Chowdhury et al. 2011; Arampatzidou & Deliyanni 2016). The negative value of entropy can be attributed to the fact that the dye molecules lose their randomness when they are adsorbed on the surface of the activated carbon (Chowdhury et al. 2011; Foo & Hameed 2012). Gibbs free energy values (−1.49 to −10.60 kJ/mol) confirmed that the adsorption of BR by SAA is a physisorption (Chowdhury et al. 2011; Garba & Rahim 2016).

Table 4

Thermodynamic parameter for adsorption of Bemacid Red by prepared carbon

T (°K) 281 298 308 328 
ΔH° (kJ.mol−1− 45.76 
ΔS° (kJ.K−1.mol−1− 0.11 
ΔG° (kJ.mol−1−1.49 −9.20 −9.90 −10.60 
T (°K) 281 298 308 328 
ΔH° (kJ.mol−1− 45.76 
ΔS° (kJ.K−1.mol−1− 0.11 
ΔG° (kJ.mol−1−1.49 −9.20 −9.90 −10.60 

CONCLUSION

In this study, activated carbon from agro-food waste was successfully used in the removal of the textile dye BR. The adsorbent obtained after physical and chemical activation has a fairly large surface area with a predominant mesoporosity.

The pH 2 and the temperature 298 K gave the maximum adsorption rate with 0.5 g of adsorbent and a contact time of 60 min.

The adsorption equilibrium is perfectly described by the Freundlich and Temkin isotherms, while the kinetics obey the pseudo-second-order model.

Negative values of ΔG°, ΔH°, and ΔS indicate that the adsorption process is spontaneous and exothermic.

The results confirm that the date stones have great potential to be transformed into high quality activated carbon. Date stone is an inexpensive material for the treatment of industrial wastewater.

The SAA, after adsorption of BR, will be regenerated thermally by pyrolysis. The organic compounds adsorbed in the activated carbon will be destroyed by thermal effect.

ACKNOWLEDGEMENTS

The corresponding author would like to thank the entire team of PHC-MAGHREB 16MAG11.

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