نوع مقاله : مقاله پژوهشی
نویسندگان
گروه علوم خاک، دانشکده کشاورزی، دانشگاه یاسوج، یاسوج ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Powdered rock phosphate may have the potential of soluble phosphate sorption because its particles are small. Phosphorus (P) sorption-desorption behavior and sorption kinetics were studied on four different fine powdered phosphate rocks (PPR), from Esfordi, Chadormalu and Yasuj mines. Sorption isotherms were evaluated by equilibrating 1 g PPR with 20 ml CaCl2- 0.01 M containing 10, 50, 100, 200, 400, 600, 800 and 1000 mg P L-1, as KH2PO4 in duplicates. Consequently, P release was studied by equilibrating the samples with 20 ml 0.01 M CaCl2. FTIR analysis was conducted on the blank samples, and those equilibrated with 1000 mg P L-1. Kinetics of phosphate sorption on PPRs was evaluated with two initial P concentrations (50 and 100 mg P L-1) and contact times of 1, 2, 4, 8, 16, 24, and 48 h with 0.01 M CaCl2 as the background solution in duplicate. Results showed that the least P sorption was around 150, and the maximum P sorption was 12000 mg kg-1 PPRs. The highest P release was around 15% of sorbed P, and releasable P was reduced to 2-3% of sorbrd P with the increase of P sorption. P sorption data showed a good fit with Freundlich and Langmuir equations. The kinetic of P sorption showed a fast reaction that rapidly diminished soluble P. Results of the present study suggest that PPRs could reduce soluble P, which is better to be considered at different usage of PPR such as incorporation with organic wastes and its biosolubilization.
کلیدواژهها [English]
The potential of powdered rock phosphate of some Iranian mine for removal of phosphate ions from aqueous solutions
EXTENDED ABSTRACT
Natural apatite, known as powdered phosphate rock (PPR), is a low price fertilizer material that has been attempted to be used instead of commercial P fertilizers. Though the direct reaction of P with PPR is not considered important, it is reported that natural apatite could sorb soluble P, either by precipitation or adsorption mechanisms. The present study was conducted to evaluate the phosphate sorption ability of finely ground phosphate rock of four Iranian mines and to quantify the q/I relationships and kinetics of P retention with PPR.
Four PPR samples of Iranian mines were tested, two samples from Esfordi mine of Yazd province, one from Chadormalu mine of Yazd province, and one from a mine, near Yasuj. In duplicate, the phosphorus sorption isotherm was evaluated by 1:20 ratio of PPR:P solution containing 10, 50, 100, 200, 400, 600, 800 and 1000 mg P L-1 (as KH2PO4). Sorption data was fitted with the linear form of Langmuir, and Freundlich models. Following the sorption the release of sorbed P was evaluated by equilibrating with 20 ml CaCl2 0.01 M. The Fourier transform infrared (FTIR) spectra of the untreated PPR samples and those treated with 1000 mg P L-1 were recorded using a JASCO FTIR 460 plus spectrometer. The kinetics of P sorption on PPR samples was studied with two initial P concentrations (50 and 100 mg P L-1) in 0.01 M CaCl2 as the background solution with a ratio of 1: 20 of PPR:P solution under laboratory temperature (20-25 ºC) and in equilibrium time of 1, 2, 4, 8, 16, 24, and 48 h shaking. Kinetic equations, including zero order, first order, Elovich, parabolic diffusion, and power function models, were used to fit the kinetic sorption.
The Ca and P content of the PPRs ranged from 41.3 to 62.6% CaO (29-44% Ca); and 6.90 to 24.50% P2O5 (3-11% P), respectively. Iron content was the highest in the raw PPR of Esfordi (around 20% Fe2O3), and the other PPRs contained 3-5 % Fe2O3. P sorption ranged from 144 to 12080 mg P kg-1 PPRs, and the highest P sorption occurred in Chadormalu, Yazd, the sample that reached up to 12000 mg kg-1. The release of sorbed P was 18-263 mg kg-1, and the highest release belonged to the PPR sample of Chadormalu, Yazd. The release quantity of the sorbed P increased linearly up to the initial concentration of 600 mg P L-1 and tended to remain constant at higher concentrations. Maximum % P release (around 15 % of the sorbed P) occurred at 10 mg P L-1. It drastically decreased by increasing P concentration and reached a minimum of about 2% above 100 mg P L-1. Phosphorus sorption data was well fitted to Freundlich and Langmuir isotherm models. The intercept of the Freundlich equation, kF, was 129-157 mg kg-1 P. The least KF belonged to the Esfordi Yazd PPR, and the highest one was observed in Chadormalu Yazd's PPR. The maximum retention capacity (bL) calculated from the Langmuir equation ranged from 15384 to 22222 mg kg-1 PPR. FTIR analysis showed that The strongest peak occurred on 1045 cm-1 for all samples, attributed to the asymmetric n3 mode of phosphate groups. The peaks in »466 n2 (bending) mode of phosphate groups, 570 and 609 asymmetric n3 mode, and P-O mode were evident in all samples. The quantity of P sorption vs. time (1 to 48h) ranged 540-1000 and 1123-2000 mg kg-1 on 50 and 100 mg P L-1, respectively. Phosphorus sorption by different PPRs, was initially fast and decreased by the increase of contact time. For all PPRs, the maximum sorption rate occurred at the first initial contact time (1 h) and decreased gradually. More than half of the final sorption quantity occurred at the initial time (1h). The content of P sorption was in the following order: Yasuj (540 mg kg-1) < Chadormalu (589 mg kg-1) -1)< raw Esfordi (742 mg kg-1); which was consistent over time. The raw Esfordi PPR had the highest P sorption rate and caused the removal of almost total soluble P in just 8 h. A similar trend with a slower kinetic rate was observed for the purified Esfordi PPR sample, which eliminated total soluble P in 16 h.
Results of the present study suggest that finely ground PPRs could rapidly retain a large quantity of soluble P, which is rarely reversible. Results presented here may be useful in the fixation of soluble P in sewage sludge or sewage effluent to prevent P transport in the environment and consequent water resources eutrophication.
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