Treatment of Boron-Containing Optoelectronic Wastewater by Adsorption and Precipitation Processes
2011
Hochschulschrift
Zugriff:
99
Treatment of boron-containing optoelectronic wastewater by adsorption and precipitation processes was investigated in this study. Adsorption process for boron removal by water treatment residuals (WTRs) was applied to dilute synthetic wastewater (ca. 20 mg/L), while precipitation process by lime (calcium hydroxide, Ca(OH)2) was applied to concentrated wastewater (ca. 750 mg/L) using both synthetic and optoelectronic wastewater. Four samples of WTRs (Al-WTR1, Al-WTR2, Al-WTR3, and Fe/Mn-WTR) were assessed as an adsorbent for boron removal. The Al-WTRs were mainly composed of Al2O3, Fe2O3, and SiO2, while Fe2O3, MnO2, Al2O3, and SiO2 were the dominant component for Fe/Mn-WTR. The adsorption reaction could be approximated by a pseudo-second-order kinetic model. The equilibrium pH (pHe) affected boron adsorption and the optimum pHe was found at pHe of 8.3±0.2 and 8.2±0.2 for Al-WTRs and Fe/Mn-WTR, respectively. The Langmuir isotherm model described the adsorption data satisfactory (R2 value average ≧ 0.990) and the batch maximum capacities were found as 0.980, 0.700, 0.190, and 0.440 mg/g using four samples, respectively at optimum pHe. Thermodynamic analysis revealed that the adsorption reaction by the WTRs was spontaneous and exothermic. The low ∆Ho value of -1.58 kJ/mol for Al-WTR1 and -8.20 kJ/mol for Fe/Mn-WTR suggested that was indicative of a physical adsorption. Electrostatic interactions and van der Waals force were proposed as major driving forces of adsorption under different pH condition. The BET specific surface area, aluminum content of Al-WTRs, and iron oxide content of Fe-WTR affected boron adsorption, as judged by the fact that Al-WTRs that have high BET surface area and aluminum content than other showed higher adsorption capacity than the others. On the other hand, the iron oxide content of Fe-/Mn-WTR also showed the same trend by using Fe-based sludge. The results of this study show that WTRs can be used as an alternative adsorbent for boron removal. Removal of high concentrated of boron from synthetic and optoelectronic wastewater by precipitation with lime (Ca(OH)2) was studied under moderate temperature (45–80oC). Pseudo-first order kinetic model fits the reaction satisfactorily. The activation energy (Ea) of the reaction was 45.1 kJ/mol, implying the reaction rate was controlled by surface chemical reaction. The calcium borate precipitate formed at 60oC was cooled to room temperature gradually and no re-dissolution of boron was found, indicating that calcium borate was a stable compound. The precipitates were characterized by SEM, XRD, and XPS, and confirmed that it was calcium borate (Ca2B2O5.H2O). Boron removal in both synthetic wastewater and optoelectronic wastewater increased with increasing pHe and stabilized at equilibrium pH of 12.4±0.1. The optimum dose of Ca(OH)2 was 10 g/L, at which 87% of boron was removed at 60oC. Experimental results showed that precipitation process using Ca(OH)2 was very effective and efficient for high concentration of boron.
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Treatment of Boron-Containing Optoelectronic Wastewater by Adsorption and Precipitation Processes
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Autor/in / Beteiligte Person: | Irawan, Chairul ; 尹海若 |
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Veröffentlichung: | 2011 |
Medientyp: | Hochschulschrift |
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