The feasibility of natural apatite for adsorptive removal of Fe3+ from aqueous solution was investigated. Batch experiments were performed as function of process parameters such as contact time, initial concentration of Fe3+, temperature, apatite dosage and pH. The natural apatite exhibited a high performance for the removal of Fe3+ from aqueous solution. The pH value clearly affects the removal mechanism of Fe3+ by natural apatite. At low pH value, dissolution/precipitation is the main effect. The effect of hydrolyzation increased with the pH value. After the pH value above 5.0, hydrolyzation is the main effect. The adsorption isotherms demonstrated that the adsorbent behaved in a favorable manner for Fe3+ adsorption. The experimental data were well fitted with Langmuir isotherm.
The feasibility of natural apatite for adsorptive removal of Fe3+ from aqueous solution was investigated. Batch experiments were performed as function of process parameters such as contact time, initial concentration of Fe3+, temperature, apatite dosage and pH. The natural apatite exhibited a high performance for the removal of Fe3+ from aqueous solution. The pH value clearly affects the removal mechanism of Fe3+ by natural apatite. At low pH value, dissolution/precipitation is the main effect. The effect of hydrolyzation increased with the pH value. After the pH value above 5.0, hydrolyzation is the main effect. The adsorption isotherms demonstrated that the adsorbent behaved in a favorable manner for Fe3+ adsorption. The experimental data were well fitted with Langmuir isotherm.
Adsorbent; Iron Removal; Apatite; Adsorption Isotherm
The tremendous increase in the use of heavy metals over the past few decades has eventually resulted in an increased flux of metallic substances in the environment. The heavy metals are of special concern because they are non-degradable and persistent. From the view of environmental protection, heavy metal ions should be removed from the source to avoid pollution of natural waters and subsequent metal accumulation in food chain. Various technological methods, such as precipitation, cementation, sedimentation, filtration, coagulation, flotation, complexing, solvent extraction, membrane separation, electrochemical technique, biological process, reverse osmosis, ion exchange and adsorption have been used for the removal of toxic heavy metals from wastewater. Among these methods, adsorption is a cost-effective technique and simple to operate [1-3]. The adsorption process usually used natural organic or inorganic materials which are particularly abundant and inexpensive. These natural materials include bark/tannin-rich materials, lignin, chitin/chitosan, dead biomass, seaweed/ algae/alginate, xanthate, zeolite, clay, fly ash, peat moss, bone gelatin beads, leaf mould, moss, iron-oxide-coated sand, modified wool and modified cotton [
The presence of iron ions as one of the heavy metals in ground and industrial water becomes toxic at high level and then may cause environmental and human health problems [5-8]. Iron ions are attracting wide research attention since they are found in many manufacturing industries such as coatings, car, aeronautic and steel industries [
The general formula of apatite is M10(XO4)6Y2 (M = Ca2+, Sr2+, Pb2+, Cd2+, Ba2+, Zn2+, Mg2+, ...; XO4 =
Ma et al. [
In this work, we presented the use of natural apatite for removal of Fe3+ from aqueous solution. The influencing factors such as pH, initial concentration, contact time, dosage of the adsorbent and temperature have been systematically investigated. And the removal mechanism of Fe3+ by natural apatite was discussed.
Natural apatite used here comes from a phosphate rock in Yichang, China. The sample was ground in a ball mill and sized by wet sieve analysis separately for experimental work. In the present studies, rock phosphate of 74 - 150 μm size range was used for the removal of Fe3+ from aqueous solution. Mineralogical analysis of rock phosphate sample reports mainly of apatite and quartz. Dolomite, calcite and iron oxide are the other associated gangue minerals.
Iron solutions were prepared by dissolving Fe(NO3)3 analytical grade. Adsorption experiments were carried out in the batch reactors (200 mL) containing natural apatite as adsorbent and 50 mL of Fe3+ solutions having different concentrations (10, 50, 100, 150 and 200 mg/L) and pH (1 - 7) was adjusted with 0.1 M HNO3 and 0.1 M NH3·H2O. In order to investigate the effect of the temperature on the adsorption, four adsorption temperatures (273, 293, 303, and 323 K) were studied. The suspensions were stirred with a magnetic stirring bar inside the reactor for different time. Then, the suspensions were filtered through a 0.45 µm membrane filter and the Fe3+ concentration in the filtrate was analyzed using UV/Vis spectrophotometer (Shimadzu, UV-2550) at 510 nm [
The morphologies and microstructures of natural apatite and the reaction production were observed by using a JSM-5510 scanning electron microscopy (JEOL, Japan). The crystalline phase of natural apatite and the reaction production were detected by powder X-ray diffraction (Bruker D8 ADVANCE, Germany) using Cu Kα radiation.
The effect of initial Fe3+ concentration in the range of 10 to 200 mg/L on adsorption was investigated (
The effect of contact time was investigated in the range of 1 min to 17 min. The result (
The effect of apatite dosage was studied in the range of 1 g/L to 28 g/L for the initial Fe3+ concentration of 200 mg/L at pH 2.85. The variation of the removal efficiency of Fe3+ ions and the pH of filter with natural apatite dosage is shown in
sorbent dosage of 28 g/l. The red brown insoluble iron hydroxide increased with increasing the dosage of natural apatite was observed in the filtration residue. That is to say, the hydrolyzation of Fe3+ increased very dramatically with increasing the dosage of natural apatite. The reason is that the addition of natural apatite can increase the pH of solution, as a result of sorption of H+ ions from the acid solution by surface active sites [
One of the most critical parameters in the adsorption process of metal ions from aqueous solutions is the pH of the medium. Hence, the effect of initial pH on removal of Fe3+ ions from aqueous solution on natural apatite was studied. The initial pH values was ranged from 1 to 7 at room temperature (20 ˚C) and the initial concentration of Fe3+ ions was chosen at 200 mg/L. The natural apatite dosage was taken as 20 g/L. The variation of the removal efficiency of Fe3+ ions and removal capability of Fe3+ ions with initial pH is shown in
sponsible to remove Fe3+ in aqueous solution.
To understand the removal mechanism, the effect of pH on the hydrolyzation of Fe3+ was investigated. The initial concentration of Fe3+ ions was 200 mg/L whereas the initial pH values were adjusted to 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 by HNO3 and NH3·H2O solutions. The solutions were filtered after stirred 10 min and the Fe3+ concentration in the filtrate was analyzed. The result (
tion increased with the pH value. After the pH value above 5.0, hydrolyzation is the predominant mechanism.
The temperature effect on removal of Fe3+ at 273 K, 293 K, 303 K, and 323 K was studied for the initial Fe3+ concentration 200 mg/L at pH 2.85.
The capacity of the adsorption isotherm plays an important role in the determination of the maximum capacity of adsorption. It also provides a panorama of course taken by the system under study in a concise form and indicates how efficiently an adsorbent will adsorb and allows an estimate of the economic viability of the adsorbent commercial applications for the specified solute. In order to adapt for the considered system, an adequate model that can reproduce the experimental results obtained. The experimental equilibrium data were fitted using Langmuir, DKR and Freundlich models (
It is obvious from
in a monolayer. Furthermore, the qm value calculated by this equation corresponds well with the experimentally obtained sorption capacity which indicates that the Langmuir equation better fits the experimental data.
Knowing the Langmuir constant, KL, the dimensionless separation factor (RL) can be derived using the expression [
where C0 (mol/dm3) denotes the initial solution concentration. RL values indicate that the sorption process is: unfavorable for RL > 1, linear for RL = 1, favorable for 0 < RL < 1, or irreversible for RL =0.
For initial Fe3+ concentration range from 1.8 × 10−4 to 3.6 × 10−3 mol/dm3, used in this study, calculated RL values were between 0.353 and 0.027, which indicated that the adsorption of Fe3+ by natural apatite was favorable.
The present investigation showed that natural apatite was an effective adsorbent for the removal of Fe3+ from aqueous solutions. The removal of Fe3+ by natural apatite was found to be dependent upon pH, contact time, initial Fe3+ concentration, dosage of the adsorbent and temperature. The removal efficiency of Fe3+ increases with the increase of adsorbent dosage and decreases with the increase of initial Fe3+ concentration. The pH value clearly affects the removal mechanism of Fe3+ by natural apatite. At low pH value, dissolution/precipitation is the predominant mechanism. The effect of hydrolyzation increased with the pH value. After the pH value above 5.0, hydrolyzation is the predominant mechanism. The equilibrium data were analyzed using Langmuir, DKR, and Freundlich isotherms. The experimental data yielded excellent fits within the following isotherms order Langmuir > DKR > Freundlich, based on its correlation coefficient values.
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