عنوان مقاله [English]
In the last few decades, due to process of shifting from traditional activities and based on manual activities to industrial ones, the need for using oil and coal and its derivatives has increased. Using these materials has caused some problems for environment as hydro carbon contamination. Soil is a major contributor to the various kinds of pollution, especially hydro carbon pollution. Due to the importance of soil in the life cycles and its vitally direct and indirect influence on all the organisms and human being, elimination of this pollutant is necessary. For this reason, some different methods have been developed. In this research, capability of soil washing by sodium dodecyl sulfate ionic detergent has been measured. In order to fulfill the existing necessity and solve this problem, a wide-ranging effort has been started from the past until now, which can be referred to the issue of washing contaminated soil as one of the issues raised. At the beginning of this technology, washing with pure water was considered and after a while, it was invalidated due to inefficiency in the tested cases. With advances in this emerging technology, the discussion of stronger solvents was explored, in which detergents became more attractive due to their lower potential toxicity and environmental degradability. Actually, the effect of major parameters on removing the hydrocarbons has been investigated and in this research has been afforded to purify polluted soil with creosote by considering actual conditions in industry.
Materials and Methods
The first sample has been taken from original soil of Razi industrial estate. It has coarse sandy loam texture with 31% clay, 11% silt and 57% of sand, pH equal 7, organic matter amount 2.3 % weight and density equal 1/8 gram per m3. Therefore, pure soil was extracted from 6 layers of soil to the depth of 0.5 m from Razi industrial area in Isfahan. Then, it was mixed by a concrete mixer specific to the block making. Afterwards, creosote was added evenly during stirring so the soil was contaminated deliberately. After storing in the laboratory for 3 weeks and homogeneity, the initial sample was chosen and its contamination was measured. This measurement was based on the amount of added oil to the certain volume of soil (about 30000 milligram in each kilogram). For avoiding error and having assurance from the amount of initial contamination, the sample was transferred to the laboratory and 25 gr of it was taken. Its hydrocarbon texture was extracted by solvent and its polar compositions were removed by passing on the silica gel absorbent. Then, a hydrocarbon was measured. The real pollutant amount of sample was 26776 milligram in each kilogram of soil. Secondary samples were chosen from basic sample, these chosen samples were washed under the different planned conditions. After finishing several complementary washing stages in different conditions, the soil samples remaining from washing were dried under different conditions. Then the amount of remained contamination in each sample was measured and recorded separately. At the next stage, the recorded results were analyzed. Stay time, temperature, pollutant concentration and washer concentration has been chosen as variable parameters.
Results and Discussion
According to the results, washing by pure water and temperature of 30°C would not be successful but by increasing temperature, the removing efficiency increased. Increasing temperature to 90°C increased the efficiency up to 18.5%. In addition, adding detergent to the environment increased the success of this method in reducing sample pollution. Increasing efficiency up to 4 g/L of detergent increased the efficiency up to 40% directly, but there was no significant change for increasing more than this amount. At this stage, the results showed that in the presence of detergent, increasing temperature caused to increase efficiency directly. The only difference was that increasing temperature (without detergent) increased efficiency directly, but in presence of detergent, increasing efficiency was significance up to 50% and after that it increased very slightly. The last studied parameter was time. These changes included increasing efficiency due to increasing time from 10 min to 20 min. Removing pollutant efficiency has been reduced by increasing time. Under all optimum conditions, in temperature of 90°C for 20 minutes and 4 g/L surfactant, Hydrocarbon removing efficiency was 61%. The economically optimum temperature is 50oC with regard to economical cases and the slight difference resulting from increase of temperature from 50 to 90°C.
Generally, the results revealed the suitability of ionic sodium dodecyl sulfate for cleaning soil under conditions of contamination. But 39 % of pollutant in polluted soil after washing by considering optimal conditions has been reminded. It must be mentioned that due to inefficiency of this amount of contamination reduction from contaminated soils for the discharge of these soils into the environment, this method can be introduced as a pollution reduction or a method for pretreatment of complementary methods.