| Soil is one of the most important parts of natural environments. It is anindispensable and non-renewable resource for humans. In recent years, however, moreand more organic pollutants enter into environments and lead to a series of pollutionand destruction of the ecological environments including soil environments, with therapid development of industry and the continuous improvement of people’s livingstandard. Especially, the behavior of petroleum pollutants in soils has been paid muchattention as one of the typical organic pollutants now.The soils in northwest of China are always unfertile with high sedimentconcentration because it is very dry and lack of rainfall. There are many oil fieldssuch as Changqing oil field, Yumen oil field in Gansu province. Petroleum pollutantsfrom the exploration of oil fields enter into environments and tend to migrate alongthe soil vadose zone, and therefore have great harmful effect on the ecologicalenvironments, especially on soil environments. In this paper, diesel oil and gasolineare used as target pollutants to research their environmental behavior on loess soils innorthwest of China. In addition, the effects of humic acid, which is extracted fromlocal soils and biochar, which is prepared with wheat straw, on the sorption of dieseloil and gasoline on loess soils are discussed as well. Furthermore, some parameterssuch as pH, temperature, the size of soil particles, and the evaporation rate of gasolineare also investigated. The aim of the work is to reveal the sorption of petroleumpollutants on loess soil, to understand the forms and migration of petroleum pollutantson loess soil. The present work helps to reveal, effectively control and removepetroleum pollutants from loess soils.The main results of this paper are as follows:1. Extraction of humic acid, preparation of biochar and their characrization.Humic acid was extracted from loess soil in northwest of China by alkali method.Biochar was prepared by burning or pyrolysis of wheat straw under anaerobiccondition. Both of them were characterized using a series of analytical methods.2. The effect of natural humic acid from local soils on the sorption of diesel oil onloess soil. In present study, thermodynamics and dynamic experiments were carried out tostudy sorption characteristics of diesel oil on northwest loess soil, especially the effectof natural humic acid which was extracted from loess soil on diesel oil sorption. Thethermodynamics experiments were carried out with/without natural humic acid at27,37, and47℃, respectively. The dynamic experiments were also carried out at27℃with/without humic acid. The results showed that the sorption of diesel oil on loesssoils were well fitted with Freundlich Isothermal Equation no matter with or withouthumic acid, but the presence of humic acid had significantly effect on sorptioncapacity of diesel oil on loess soil. The sorption quantity of diesel oil on loess soildecreased from12.0mg·g-1to7.05mg·g-1in the presence of10mL40mg·L-1humicacid at27℃. The sorption capacity of diesel oil on loess soil also reduced from12.0mg·g-1to4.23mg·g-1with increase of temperature from27℃to47℃, indicating thatthe sorption of diesel oil on loess soil was a spontaneous exothermic process. Thesorption kinetics curve of diesel oil was best fitted with Elovich Kinetics Equation,and was also fitted with Double-constant Equation. The sorption balance could bereached rapidly within6h in the presence/absence of humic acid. In addition, someparameters, such as pH and soil particle size, were discussed in this chapter. Theresults showed that the sorption capacity of diesel oil decreased with increasing of pH,and the sorption quantity of diesel oil was increased with decreasing of soil particlesize.3. Study on sorption characteristics of gasoline on loess soil.Dynamic and thermodynamics experiments were carried out to study sorptioncharacteristics of gasoline on loess soil in Northwest China in this work. The effect ofnatural humic acid on sorption behavior of gasoline on loess soil was investigated.The results showed that the sorption balance of gasoline on loess soil was reachedwithin6h. The sorption kinetics of gasoline was well fitted with Elovich kineticsequation and the sorption thermodynamics was well fitted with Freundlich isothermalequation in the presence/absence of humic acid. However, the presence of humic acidresulted in a decrease of the sorption capacity of gasoline on loess soil. When thetemperature increased from25℃to45℃, the sorption capacity of gasoline decreasedfrom6.30mg·g-1to1.37mg·g-1, indicating a spontaneous exothermic process of the sorption of gasoline on loess soil. Also, higher pH and larger soil particle size lead todecreased sorption capacity of gasoline, respectively. In addition, the evaporation rateof gasoline adsorbed on soil samples was slower than that of pure gasoline at ambienttemperature. Furthermore, the relationship between evaporation rate and time waswell fitted with logarithmic expression.4. Effect of biochar on the sorption characteristic of diesel oil and gasoline onloess soil.In this chapter, batch experiments were performed to understand the sorptionkinetics and thermodynamics of diesel oil and gasoline on loess soil. The resultsshowed that sorption balance of diesel oil and gasoline on loess soil was both reachedin a relatively short time. The sorption kinetics of diesel oil and gasoline were wellfitted with Elovich kinetics equation and the sorption thermodynamics were fittedwell with Freundlich isothermal equation in presence/absence of biochar. However,the presence of biochar had obvious effect on the sorption capacity of diesel oil andgasoline on loess soil. The sorption quantity of diesel oil on loess soil increased from13.6mg·g-1to20.1mg·g-1、23.7mg·g-1in the presence of0.0500mg BC-400andBC-600at25℃, respectively. Accordingly, the sorption quantity of gasoline alsoincreased from5.44mg·g-1to11.9mg·g-1and17.2mg·g-1, respectively. Moreover,pH had a certain effect on the sorption of diesel oil and gasoline on loess soil. While itseemed that the presence of biochar had little effect on the trend of pH vs. sorptioncapacity. |
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