This paper outlines the synthesis of maghemite from raw iron waste obtained in an iron mill dumpsite around Ogun state, Nigeria. Magnetite was synthesized from the ferrous precursor obtained by digesting the iron waste with concentrated H 2SO 4. Transformation of magnetite to maghemite was done by heating the magnetite obtained in an oven at 200°C. To determine the absorption capacity of the synthesized maghemite sample, a stock solution of As(III) was used for the absorption. Absorption spectrum shows higher absorption of γ-Fe 3O 4 at higher concentration of As(III). Maximum absorption obtained is 14 mg/g. Estimated yield of γ-Fe 3O 4 was 32%; however a low, further study promises to improve the yield value. The study shows γ-Fe 3O 4 to be a good absorbent for heavy metals.
Iron oxide generally exists in different structures and forms with different useful applications ranging from geological to nanoscale technology; the most common however are α-Fe2O3 (hematite), γ-Fe2O3 (maghemite), Fe3O4 (magnetite) and Fe1−xO (wustite); the less commonly found are β- and ε-Fe2O3 [
However, a present review of the various synthesis methods available for maghemite nanoparticles growth shows co-precipitation, thermal decomposition, hydrothermal synthesis, microemulsion, sonochemical synthesis, and sonochemical as the most common methods; other methods such as electrochemical synthesis, laser pyrolysis techniques are not common [
Metals are natural components of the environment including soil but they are of great concern when they are being added continuously. Nigeria as a country has a lot of iron mining and other allied iron processing companies. Unfortunately, only few of these companies have a standard way of disposing their waste iron scrap. This has a devastating effect on the environment with a long-term impact [
Experiment was carried out according to Legodi et al. (2007) [
20 g of the ferrous precursor was added to 120 ml of deionized water. The mixture was stirred gently. A green precipitate solution of Fe2+ was formed and filtered off. 25% NH4OH, prepared by making up 25 ml of concentrated ammonia in a 100 ml standard flask with deionized water was added to the filtrate and allow to age for 20 hours and filtered before washing with deionized water. On drying, a crystalline, fine, black particle of magnetite was obtained. Finally, the magnetite obtained above was oven heated at 200˚C for two hours according to the equation below (Equation (2.2)). Maghemite particles, with a light brown coloration were obtained. The experiment was performed inside a glove box to prevent any possible oxygen contamination
Two batches (A and B) of various standards, 10, 20, 30, 40, 50, 100, 200, 300, 400, 500, and 1000 ppm of As(III) solution was prepared. Batch A was taken as the standard solutions with which the amount of As(III) sorbed were referenced 0.5 g of the maghemite particles synthesized was weighed into each concentration of the second batch and stirred vigorously in a mechanical stirrer until complete dispersion was observed. Atomic absorption spectrophotometry was used in determining the actual concentration of As(III) in both batches.
The absorption data obtained for both batches are tabulated as in
The concentration of As(III) in the stock after the absorption was also determine and the result is presented in
S/N | Standards (ppm) | Absorbance |
---|---|---|
1 | 10 | 0.60 |
2 | 20 | 0.70 |
3 | 40 | 0.75 |
4 | 50 | 0.80 |
5 | 100 | 0.95 |
6 | 200 | 1.15 |
7 | 300 | 1.30 |
8 | 400 | 1.35 |
9 | 500 | 1,45 |
10 | 1000 | 1.60 |
S/N | Standards (ppm) | Absorbance |
---|---|---|
1 | 10 | 0 |
2 | 20 | 0 |
3 | 40 | 0.02 |
4 | 50 | 0.07 |
5 | 100 | 0.13 |
6 | 200 | 0.53 |
7 | 300 | 0.63 |
8 | 400 | 0.72 |
9 | 500 | 0.85 |
10 | 1000 | 1.15 |
S/N | Standards | Absorbance | Concentration | Qsorbed (mg/g) |
---|---|---|---|---|
1 | 40 | 0.02 | 0 | 0 |
2 | 50 | 0.07 | 0 | 0 |
3 | 100 | 0.13 | 5 | 2 |
4 | 200 | 0.53 | 15 | 3.86 |
5 | 300 | 0.63 | 25 | 5.8 |
6 | 400 | 0.72 | 98 | 6.04 |
7 | 500 | 0.85 | 130 | 7.4 |
8 | 1000 | 1.15 | 300 | 14 |
where Qsorbed is the amount of maghemite iron adsorbed, v is the volume of the stock solution taken for analysis, Ci is the initial concentration of the As(III), Cf is the final concentration of the As(III) after the absorption and m is the mass of the maghemite sample used for the absorbtion experiment (
A plot of Qsorbed (mg/g) against concentration of arsenic (ppm) (see
Yield Calculation
Mass of iron waste used 60 g
Mass of ferrous Precursors obtained after digestion 70 g
Residue obtained after washing with excess water and filtering 50.22 g
This implies that Mass of Fe3+ that’s dissolved 70 g - 50.55 g 19.78 g
Mass of Magnetite obtained after drying 9.02 g
From the equation of reaction (2.1 above),
3 moles of Fe3+ (168 g/mol) 2 moles of Fe3O4 (233 g/mol)
⟹ Number of moles of Fe3O4 produced = [(19.78 g ´ 3 mol)/168 g∙mol−1]/3 mol
⟹ Experimentally, 0.118 mole of Fe3O4was obtained
⟹ 27.376g (Molar mass of Fe3O4 ⟹ 232 g∙mol−1)
Percentage yield of Fe3O4 =
One mole Fe3O4 (232 g/mol−1) ⟹ one mole of (160 g∙mol−1) γ-Fe2O3
⟹ 9.02 g of Fe3O4 ⟹ [9.02 g ´ 160 g∙mol−1]/232 g∙mol−1 ⟹ 6.220 g
Percentage of γ-Fe2O3 ⟹
It has been shown that maghemite can be successfully synthesized from waste iron by transforming the magnetite obtained from the ferrous precursor. Sorption experiment proved maghemite to be a good absorbent for As(III). Other heavy metals such as Cr, Pb, etc. were however not studied. The absorption was low at lower concentration (10, 20, 30, 40, 50 ppm). More As(III) were sorbed at higher concentration. Experimental yield obtained for mghmite finally synthesized was low (32%). We believe that this can be improved with more studies. Heavy metals present in most water, waste and other environmental surfaces can be successfully removed at a low cost and pollution reduction.
John AdeolaAdegoke,I. AdegokeHalimat, (2016) Absorption Studies of Arsenic Using Maghemite Crystals Synthesized from Iron Waste Extracted from Ogun State Iron Mill Dumpsite. American Journal of Analytical Chemistry,07,294-298. doi: 10.4236/ajac.2016.73027