In the present study, we investigated the performance of clay mineral originated from a dam situated in Morocco (Agadir city), as natural, low-cost, alternative and eco-friendly adsorbent for removal of nitrates ions from aqueous solution within a batch process. The clay was characterized by X-ray diffraction, Scanning Electron Microscopy (SEM), Dispersive Energy of Spectroscopy (EDS), Fourier Transform Infrared (FTIR) and surface area analysis (BET). The effects of various experimental parameters are examined such as contact time, initial concentration of pollutant, adsorbent mass and solution pH. The removal of nitrate was 71.89% at natural pH (pH = 5.1) using 1 g/l of adsorbent in 500 ml of nitrate solution having initial concentration of 300 mg/l (effect of contact time). Adsorption kinetic study revealed that the adsorption process followed first order kinetic. Theoretical correlation of the experimental equilibrium adsorption data for the Nitrate-New Clay system was properly explained by the Langmuir isotherm model. The maximum adsorption capacity was Q m, exp = 244.06 mg/g at 20℃ and at natural pH (with Q m, cal = 250 mg/g). An increase in adsorbent dosage increased the percent removal of nitrate, R = 1 g/l was considered as optimum dose and was used for further study. The pH heavily affected the adsorption capacity, and the percentage removal was found to decrease with increase in pH. The obtained results indicated that this New Clay (NC) was very good adsorbent for NO 3 -, interesting alternative material with respect to more costly adsorbent used, and could be used as a highly efficient adsorbent for the separation of nitrate from drinking or waste water.
Nitrate contamination in groundwater has become an ever increasing and serious environmental threat since 1970s [
Therefore, numerous techniques for the removal of nitrate from water samples have been reported. These include biological de-nitrification [
The main aim of our study is to determine the adsorption capacity of locally available natural clay materials originated from a dam situated in Morocco (Agadir city) and to remove nitrate from its aqueous solution. Hence, the effect of various parameters on the adsorption process has been investigated: contact time, solution pH, and mass of adsorbent and nitrate concentration. The results are presented and discussed in this study. It is interesting to note that the adsorption of cationic and anionic dyes on this support is examined in our laboratory [
Potassium nitrate used in the present study was of analytical grade and was obtained from Sigma-Aldrich. 1000 mg/l stock solution of nitrate was prepared. The required concentration of nitrate solution was obtained by serial dilution of the stock nitrate solution.
The untreated clay used in this work is crushed then sifted in order to get fractions <80 μm. Afterwards, the support is rinsed many times with distilled water, of pH = 6.5 and of conductivity = 1.1 μS. After every rinse, the clay is put in a sedimentation test, and during one hour of decantation, we recover the two thirds of supernatant volume. Finally, it is placed in an oven between 110˚C and 120˚C during 24 hrs, before being subjected to different adsorptions.
The ability of our new clay mineral (NC) to adsorb nitrate ion was tested at different conditions (
Experiments | Conditions | ||||
---|---|---|---|---|---|
Solution pH | NC Dose (g/l) | Concentration (mg/l) | Mixing Time (min) | Volume (ml) | |
Effect of contact time | pHnatural = 5.1 | 1 | 300 | 300 | 500 |
Effect of initial solution pH | 2 - 10 | 1 | 300 | 180 | 100 |
Effect of adsorbent dose | pHnatural = 5.1 | 0.2 - 2 | 300 | 180 | 100 |
Effect of initial nitrate concentration | pHnatural = 5.1 | 1 | 100 - 450 | 180 | 100 |
easily applied [
with:
Qe: Quantity of nitrate adsorbed per gram of adsorbent (mg/g);
C0: Initial concentration (mg/1);
Ce: Equilibrium concentration (mg/l);
R: Mass of adsorbent per liter of aqueous solution (g/1).
X-ray powder diffraction pattern was obtained using the diffractometer XPERT-PRO type PW3064, with copper anticathode. The spectrum of XRD shows that the untreated clay contains a large amount of the Kaolinite (38%) and Illite (24%) followed by Quartz (20%) and Calcite (18%) (
The morphology of the clay powder particles was observed by scanning electron microscopy (SEM, using Zeiss Ultra Plus) with a coupled energy dispersive spectroscopy (EDS), at 5 kV, after gold coating. The morphological aspects of the clay particles are outlined in
In order to determine the surface functional groups, the Fourier Transform Infrared (FTIR) spectrum of the NC was obtained by using a Bruker Vertex 70 spectrophotometer, at a resolution of 4 cm−1 and averaging over 20 scans, in the range 400 - 4000 cm−1.
The FTIR spectrum of our clay was depicted in
Elements | O | C | Na | Mg | Al | Si | K | Ca | Ti | Fe |
---|---|---|---|---|---|---|---|---|---|---|
% Atomic | 67.71 | 3.27 | 0.26 | 1.03 | 7.20 | 14.82 | 1.36 | 2.29 | 0.26 | 1.79 |
% Mass | 53.58 | 1.94 | 0.30 | 1.24 | 9.61 | 20.59 | 2.63 | 4.53 | 0.62 | 4.94 |
Adsorption kinetic is an important characteristic for evaluating the efficiency of adsorption. The kinetic behavior of this process was studied at natural pH (
The kinetics of adsorption data was processed to understand the dynamics of adsorption process in terms of the order of rate constant. Two kinetic models were applied to the adsorption kinetic data in order to investigate the behavior of adsorption process of nitrates onto our clay. These models are the pseudo-first-order and pseudo-second-order models.
The pseudo-first-order equation is given by [
where qe and qt are the amounts of nitrate adsorbed (mg/g) at equilibrium and at time t (min), respectively, and k1 (l/min) is the rate constant of first-order adsorption.
The pseudo-second order process can be written as follows [
where k2 g/(min.mg) is the rate constant of second-order adsorption. The fit of these models was checked by each linear plot of ln(qe − qt) versus t (
qe,exp (mg/g) | First-order kinetic model | Second-order kinetic model | ||||
---|---|---|---|---|---|---|
215.69 | k1 (l/min) | qe,cal (mg/g) | R2 | k2 (g/mg min) | qe,cal (mg/g) | R2 |
0.020 | 224.752 | 0.998 | 3.515 × 10−5 | 333.333 | 0.928 |
The effect of initial solution pH on nitrate removal is illustrated in
For studying the effect of mass of adsorbent on nitrate adsorption onto our clay, experiments were performed with varying amounts of adsorbent, ranging from 0.2 to 2 g/l (
The influence of initial nitrate concentration on adsorption percentage was estimated (
Adsorption isotherms indicate distribution of adsorbate between solution and adsorbent at the equilibrium state of the adsorption process [
The Langmuir isotherm is based on the assumptions that adsorption takes place at specific homogeneous sites within the adsorbent, there is no significant interaction among adsorbed species, and the adsorbent is saturated after the formation of one layer of adsorbate on the surface of adsorbent [
The linearized form of Equation (5) can be written as Equation (6):
where Ce is the equilibrium concentration of the remaining solute in the solution (mg/l), Qe is the amount of the solute adsorbed per mass unit of adsorbent at equilibrium (mg/g), Qm is the amount of adsorbate per mass unit of adsorbent at complete monolayer coverage (mg/g), and KL (l/mg) is a Langmuir constant. In this work, we used the linear form of Langmuir isotherm equation and therefore, a plot 1/Qe versus 1/Ce should indicate a straight line. The Qm and KL values were calculated from the slopes (1/Qm) and intercepts (1/KL∙Qm) of linear plots of 1/Qe versus 1/Ce (
One of the essential characteristics of the Langmuir model could be expressed by a dimensionless constant called equilibrium parameter, RL which is determined as follows [
where C0 is the initial nitrate concentration (mg/l). The value of RL indicates the type of isotherm to be irreversible
Qm, exp (mg/g) | Langmuir parameters | Freundlich parameters | ||||||
---|---|---|---|---|---|---|---|---|
Qm, cal (mg/g) | KL (l/mg) | R2 | RL | KF ((mg/g) (1/mg) 1/n) | 1/n | R2 | ||
244.06 | 250 | 0.307 | 0.992 | 7.186 × 10−3 ≤ RL ≤ 0.031 | 99.683 | 0.181 | 0.908 | |
(RL = 0), favorable (0 < RL < 1), linear (RL = 1), or unfavorable (RL > 1). RL values are well within the defined range (
The Freundlich isotherm was proposed as the earliest empirical equation and was shown to be consistent with exponential distribution of active centers, characteristic of heterogeneous surfaces [
Logarithmic form of Equation (8) can be written as Equation (9):
where Kf ((mg/g) (1/mg) 1/n) and n are Freundlich adsorption isotherm constants, the values of Kf and 1/n are determined from the intercept and slope of the linear regressions and are presented in
This study investigated the adsorption characteristics and suitability of our new natural clay mineral (NC) as potential adsorbent for the removal of nitrate from aqueous solutions using batch technique. The results showed that this clay could be used as potential sorbent and it was highly effective as low-cost adsorbent for the removal of nitrates ions from aqueous solutions. The batch study parameters, pH of solution, mass of adsorbent, initial solution concentration and contact time were found to be effective on the adsorption processes. The adsorption equilibrium was attained within 3 hrs. From the studies conducted, it was established that pseudo-first-order kinetic model described the kinetic rate. The percentage removal was found to decrease with increase in pH. The increase in adsorbent dosage increased the percent removal of nitrate due to the increase in adsorbent surface area in adsorbent dosage. The equilibrium data fitted well the Langmuir isotherm equation and this adsorbent showed large uptake capacity of nitrate (Qm, cal = 250 mg/g, Qm, exp = 244.06 mg/g). Our clay was a potential candidate as a highly efficient adsorbent for remediation of nitrate contaminated water owing to its exceptional uptake capacity as well as high selectivity for this anionic contaminant.
MahmoudEl Ouardi,SamirQourzal,SaidAlahiane,AliAssabbane,JamaaDouch, (2015) Effective Removal of Nitrates Ions from Aqueous Solution Using New Clay as Potential Low-Cost Adsorbent. Journal of Encapsulation and Adsorption Sciences,05,178-190. doi: 10.4236/jeas.2015.54015