Chemical Engineering and Processing: Process Intensification
Ammonium ion adsorption with sepiolite: use of transient uptake method
Introduction
The industrial, agricultural and domestic wastes, due to the rapid development in technology and urbanization, are withdrawn to several receivers. Generally, this withdrawal is done to the nearest water sources such as rivers, lakes and seas. Control of water pollution has rather importance for both organisms, who live in water and those who benefit from water. The presence of excess nitrogen and its compounds causes the demolition of the environment, so the nitrogenous compounds take an important place in water pollution and it is well known that they cause serious diseases. Therefore, control of them in water has vital importance. The ammonia and ammonium ions are the more commonly encountered nitrogenous compounds in wastewater.
The wastewater treatment includes one or a combination of physical, chemical, and biological purification methods in order to recover some, or all of the lost water properties due to the several uses and to make the water receivers, in which the wastewater is discharged, not to destroy the physical and ecological properties of the environment. Among several removal technologies, adsorption and ion exchange with natural clays have great importance due to the ease of operation and comparable low cost of application. Most of the clays, which are hydrated aluminum–silicate minerals, have shown affinity to ammonium and they are potentially useful in removing ammonia contaminant and undesired odors from the environment.
Several works related to the wastewater treatment using bentonite, sepiolite and clinoptilolite from many different deposits have been cited in the literature. Suzuki and Ha [1], investigated the ion exchange and the equilibrium for NH4+–Na+, NH4+–K+, and NH4+–Ca2+ systems in the channels of clinoptilolite at room temperature. It was observed that clinoptilolite has a higher selectivity for ammonium, relative to the sodium and calcium ions. The effective diffusion coefficient for ammonium and sodium ions in clinoptilolite was observed around 4–5×10−12 m2/s. Bernal and Lopez [2] studied the ammonia and ammonium removal using clinoptilolite and sepiolite. They showed that sepiolite also had comparable ammonium removal capacity. Booker et al. [3] observed that NH4–N concentration decreased below 1 mg/l for the sewage treatment having the concentration ranging from 25 to 50 mg NH4–N/l using natural zeolite. They also observed that intraparticle diffusion controlled the adsorption rate and data were in an agreement with Vermulen approximation yielding the diffusion coefficient around 3×10−12 m2/s. Noda [4] observed that in the basic media, the ammonium removal rate from highly concentrated solutions by mordenite was obtained more than 95%. Ruiz et al. [5] also showed that ammonium removal was increased with alkaline treatment of bentonite. In the absence of competitive ions, high removal efficiencies were obtained. Over 87% removal of ammonia was achieved from domestic dairy and piggery wastewaters using clinoptilolite and mordinite having particle sizes ranging between 0.25 and 2.83 mm [6]. During the treatment of pig slurry with sepiolite, a decrease in the ammonium nitrogen and total nitrogen concentration was observed while the removal of microorganisms was also achieved [7]. Veigh and Weatherley [8] observed around 90% removal of influent ammonia in the continuous packed bed operation using clinoptilolite. Rozic et al. [9] obtained around 50% ammoniacal nitrogen removal at low solution concentration using zeolite and natural clays. They also observed the decrease of removal efficiency with increasing initial concentration. Lind et al. [10] studied the nutrient recovery from human urine using zeolite and natural clinoptilolite. Around 65–80% nitrogen capture was obtained by adsorption in combination with crystallization by MgO addition.
Sepiolite, which is a zeolite like clay mineral, provides high specific surface area. So, it has many industrial applications as an adsorbent. The high capacity values were also observed for the heavy metal ions removal and wastewater treatment using sepiolite [11], [12], [13], [14], [15], [16]. The abundance and availability of sepiolite mineral reserves as a raw material source and its relatively low cost, guarantee its continued utilization in the future, and most of the world sepiolite reserves are found in Turkey. The other way the good results cited in the listed earlier studies on wastewater treatment and ammonium ion removal with sepiolite forces to make relevant investigation.
Section snippets
Experimental part
The ammonium removal was investigated using sepiolite from Tacir region, a small town in Middle Anatolia. The chemical analysis of the calcined mineral determined by X-Cem spectrophotometer was given in Table 1. The surface area determined under continuous nitrogen–helium flow using Quantochrome Direct Surface Analyzer was 263 m2/g at 100°C. Total porosity determined by He-displacement and mercury intrusion technique was around 0.69 at 100°C. Detailed characterization studies of the sepiolite
Variation of solution concentration and adsorption equilibrium
The variations of modified ammonium ion concentration Ct/C0 (the ratio of ammonium ion concentration in the solution at any time to the initial ammonium ion concentration) with respect to adsorption time were given in Fig. 1, Fig. 2 for w/v values of 1/70 and 1/35 g sepiolite/ml solution, respectively. The variations of ammonium ion concentration in the solution with time were also shown in Fig. 3, Fig. 4 for w/v of 1/70 and 1/35 g sepiolite/ml solution, respectively. A decrease in solution
Conclusions
The capacity of sepiolite to ammonium was 3.50 mmol NH4+/g within the performed experimental conditions. Around 60% ammonium ion removal was achieved. The adsorption rate was very high especially at early stages of the treatment. The used exponential decrease for the variation of the solution ammonium concentration in the solution fitted the data very well. The effective diffusion coefficient of ammonium ion in the channels of sepiolite was around 1.4×10−10 m2/s.
Acknowledgements
This work was partially funded by Government Project of DPT/96K 120780 and Turkish Scientific Technical Research Council, TÜBITAK-MISAG-A-49.
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