ISSN 0147-6874, Moscow University Soil Science Bulletin, 2017, Vol. 72, No. 3, pp. 119–124. © Allerton Press, Inc., 2017. Original Russian Text © E.S. Chechetko, I.I. Tolpeshta, Yu.A. Zavgorodnyaya, 2017, published in Vestnik Moskovskogo Universiteta, Seriya 17: Pochvovedenie, 2017, No. 3, pp. 33–38.
ECOLOGICAL SAFETY
Application of Dodecyltrimethylammonium-Modified Bentonite for Water Purification from Oil and Water-Soluble Oil Components E. S. Chechetko*, I. I. Tolpeshta**, and Yu. A. Zavgorodnyaya*** Department of Soil Science, Moscow State University, Moscow, 119991 Russia *e-mail:
[email protected], **e-mail:
[email protected], ***e-mail:
[email protected] Received February 15, 2017
Abstract—A sorbent of oil and water-dissolved oil components is prepared from organobentonite, and its ability to absorb those products is assessed. Bentonite modified with dodecyltrimethylammonium added at a rate of 0.5 CEC was found to absorb 1.6 times as many oil components as nonmodified bentonite. The obtained sorbent has good flotage characteristics due to the formation of a durable film on the surface of oil spots, which can be easily removed. The sorbent is effective in extracting water-soluble oil compounds and has no toxic effect on Paramecium caudatum and Ceriodaphnia affinis. When the temperature is lowered from 22 to 10°, sorbent efficiency is reduced. Keywords: oil pollution, bentonite organoclay, water-soluble oil components DOI: 10.3103/S0147687417030036
INTRODUCTION On the surface of a waterbody, oil forms a film and an emulsion, and some of its components are dissolved in the water. The latter include arenes (benzene, toluene, xylene, and ethylbenzene); low-molecular polycyclic aromatic compounds; some naphthenic aromatic, sulfur, and nitrogen compounds; pentane and isopentane; and cycloparaffins (cyclopentane and cyclohexane) [10]. Water-soluble oil components, 80–90% of which can constitute aromatic compounds [3], have a toxic effect on numerous representatives of water biota [12, 18, 20]. For sorption of oil from the water surface, various clay-based sorbents are widely used. Their main requirements are high oil capacity, buoyancy, large specific surface area, and hydrophobicity. To improve the sorption characteristics of layered aluminosilicates with respect to oil components, minerals are modified with organic compounds capable of hydrophobizing the surfaces of clays [9]. One a modification is saturation with alkylammonium cations [4, 11, 13, 17, 21]. Nonpolar organic compounds are sorbed on hydrophobic areas of the surfactant molecule [22]. Despite the fact that, at present, the sorbent market is diverse, work on creating new, cheaper, and more effective forms continues unabated. The aim of this work is to create a bentonite-based sorbent capable of removing oil and its components
from the surface and volume of water at different temperatures, as well as to determine its oil capacity. MATERIALS AND METHODS The study object the is the bentonite from the Sarigyukh deposit (Tavush oblast, Republic of Armenia), which was provided for research by BentoGroupMinerals. According to their data, the size of its particles, represented mainly by aggregates, varies from 0.5 to 2.0 mm. Clay contains about 90% montmorillonite [14]. The original bentonite (Ca,Mg-bentonite) was ground in an agate mortar and put through a sieve with a gage of 0.5 mm. The dimensions of ground bentonite fractions were measured by laser diffractometry on a FRITSCH Analysette 22 instrument with preliminary ultrasound treatment of the suspension in distilled water using a 20 kHz BRANSON 250 W ultrasonic disperser. The gross composition of the clay was determined by the atomic emission method with inductively coupled plasma on an Optima-4300 DV spectrometer (PerkinElmer, United States); the total Fe2+ content was determined by the titrimetric method. X-ray diffractometry was used to study the mineralogical composition of clay and the degree of its modification by the surfactant. The survey was carried out on the DRON-3 instrument in the following mode: Cu–Kαradiation, filtered Ni, voltage and current in the tube
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35 kV and 20 mA, respectively. The X-ray survey used oriented preparations of Na-bentonite in original form saturated with ethylene glycol and calcined for 2 h at 350 and 550° and bentonite treated with dodecyltrimethylammonium bromide. Organognline (DDTMA-bentonite) was prepared by saturation with alkylammonium cations from a dodecyltrimethylammonium bromide solution at a rate of 50 (DDTMA-bentonite 0.5 CEC) and 100% (DDTMA-bentonite-1 CEC) cation exchange capacity (CEC) [16]. Before treatment with the surfactant, the carbonates were removed from the clay with a 10% HCl solution and the clay was transferred to the Na form (Na-bentonite). In the experiment on clay sorption of water-soluble oil components, we used crude oil from the Grachevsky deposit, which belongs to the Volga–Ural oil and gas province of the Republic of Bashkortostan. The oil of this deposit belongs to light paraffinic sulfur. The content of light fractions from the beginning of boiling to 300° on average is 45%; of hydrogen sulphide, up to 0.8; of nitrogen, from 5.6 to 7.1; and the associated gas contains up to 50% methane by volume [15]. Two series of experiments were carried out. In the first, at temperatures of 10 and 22°, the oil capacity of the native and modified clay forms was determined. For this, clay was added in portions to 2.2 g of oil placed on the bottom of a porcelain cup, until all oil was absorbed by the sorbent. The second series tested the ability of bentonite to remove oil from the surface and the volume of water. For this, 2.2 g of oil were added to glass beakers with 100 mL of distilled water, which yielded a film about 4 mm thick on the surface of the water. The amount of sorbent calculated (based on the determined oil content) was poured onto the surface of the oil film and collected after 10 min, and the presence or absence of the iridescent film was detected visually. Four variants of the experiment were used. Distilled water with oil without addition of sorbent was used as the control (variant 1). In variants 2– 4, Ca,Mg-bentonite, DDTMA-bentonite-0.5 CEC, and DDTMA-bentonite-1 CEC, respectively, were used. To determine the concentration of dissolved oil components in the water, an aliquot of the sample was taken with a syringe, with the needle placed into the middle of the beaker so as not to touch the residue of the iridescent film on the surface of the water where it was present. From the liquid phase, petroleum products (PPs) were recovered with hexane at a 5 : 1 water/hexane ratio. Below, PP is used in an analytical sense; i.e., PPs are compounds extracted from water with hexane. The PP content in the hexane extract was determined by fluorescence spectroscopy, according to Federal Level Environmental Regulatory Document 14.1:2:4.128-98, on an LS 45 luminescence spectrom-
eter with an excitation duration of 270 nm. The concentration was estimated from the integral fluorescence in the range from 300 to 350 nm. To calibrate the instrument, GSO 7117–94 Standard Sample of the Content of Petroleum Products in a Water-Soluble Matrix was used. The composition of water-soluble oil components was determined by GC-mass spectrometry on an Agilent 6890 gas chromatograph with a DB-1ms 30 m × 0.25 mm × 0.25 μm capillary column and an Agilent 5973 mass spectrometer detector in full ion current scanning mode. The compounds were identified by mass spectra (NIST Mass Spectral Library, 2.0 ver., 2008). Quaternary ammonium salts can exhibit toxic effects against representatives of water biota (fish, daphnia, algae, etc.) [23, 25]. Despite the fact that these salts undergo easy biodegradation under aerobic conditions [23], the clay modified with dodecyltrimethylammonium was tested for toxicity. Biotesting was carried out using two test cultures: Paramecium caudatum and Ceriodaphnia affinis [2, 6]. RESULTS AND DISCUSSION Granulometric, Chemical, and Mineralogical Composition of Bentonite Ground bentonite consists of particles with a diameter of 1 to 5 μm, 63% of which are dominated by particles with a diameter of about 1.6 μm (Table 1, Fig. 1). After the removal of carbonates from Ca,Mg-bentonite and its saturation with sodium cations in bentonite clay, an insignificant amount of calcium remains. The sample contains about 4% of Mg and more than 5.4% of Fe3+ oxides (mass percent) (Table 2). Modification of Bentonite The original bentonite consists mainly of montmorillonite and contains an admixture of calcite, quartz, and zeolites (Fig. 2). The interplanar distance on 1.2 nm corresponds to montmorillonite saturated with monovalent cations [19]. When montmorillonite is saturated with quaternary ammonium salts, the alkyl ammonium cation is fixed to the interlayer as a result of cation exchange to Na+, which leads to an increase in d/n. Saturation of Na-bentonite with dodecyltrimethylammonium broTable 1. Particle size distribution in sample of ground bentonite Particle size, >250 250–50 50–10 10–5 5–1 μm Fraction content, %
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