جستجوی مقالات مرتبط با کلیدواژه « نیترات سرب » در نشریات گروه « عمران »

Soil pollution due to various factors is one of the world's problems in different countries, especially industrialized countries, which has attracted much attention in the form of various researches. To solve this problem, in this study, metakaolin was used to stabilize low-plasticity (CL) clay contaminated with lead and zinc nitrate. The present study consists of two main stages. The first stage examines the soil to identify the most critical concentrations of contaminated soils and soils contaminated with lead nitrate and zinc nitrate in a ratio of 1: 1 and with concentrations of 1000, 5000 and 10000 ppm with a curing time of 7 days. The results obtained in the first stage showed that increasing the concentration of pollutants has a negative effect on soil geotechnical parameters, which can be reduced to the maximum uniaxial compressive strength and reduced soil CBR resistance. This step aimed to identify the most critical concentration of contaminated soil, which was 100 ppm. The second stage examines the resistance tests of contaminated soil with a concentration of 10000 ppm and its stabilization with metakaolin at a rate of 5% by weight and with a curing time of 7, 14 and 28 days. The purpose of curing time is to investigate the effect of time on soil geotechnical parameters during the presence of metakaolin in the soil. In general, according to the results of these experiments, the maximum uniaxial compressive strength and soil CBR strength increased with increasing curing time. As the curing time increases, the soil adhesion increases and consequently the compressive strength of the soil increases.

In past few decades, the expansion of industrial areas and increasing the effluents has led to increase the contamination of heavy metal in soil and groundwater resources. Adsorption is one of the most important processes that affecting in the leakage of contamination. Prevention the leakage of heavy metal contamination and economic considerations are always one of the basic principles in designs. Thus the use of natural and inexpensive adsorbents ,like clay and zeolite, is feasible procedure for the improvement of contaminated soil. In this study, with triaxial tests, the behavior of mixed sandy clay (base composition) with 10% of different low plasticity (kaolinite and zeolite) and high plasticity (bentonite) adsorbents is studied in both contaminated and uncontaminated states. The results show, as the concentration of lead heavy metal increase in soils with low plasticity adsorbent, the shear strength and internal friction angle decrease by about 20% and 14% respectively. As the type of adsorbent mineral changed, the resistance parameters of contaminated soil show different trend. Increasing the concentration of lead in the soil with bentonite adsorbent, has led to form the flocculation structure and it cause shear strength and internal friction angle increase a bout 18% than uncontaminated state. Also, cohesion in compositions with low and high adsorbent increases and decreases by about 30% and 19%, respectively.

By the expansion of the industrial zones, heavy metals enter the environment through industrial wastewater or leakage from storage tanks, which contaminates the soil and groundwater. The leakage of heavy metals such as lead, zinc, cadmium and etc. is not only an environmental crises, but also causes changes in soil shear resistance parameters. Type of soil and initial concentration of contamination are most prominent parameters that affect the behavior of contaminated soils.In this research, with Triaxial tests, the behavior of sandy soils with different percentages of kaolinite in two cases of non-contaminated and contaminated with lead is investigated. It can be seen that by increasing the lead concentration, the hydrogen bonding between kaolinite particles reduce and it decreases the resistance of contaminated soils. By increasing the concentration of heavy metals up to 20,000 ppm, the shear resistance of clayey sand with 15% and 25% kaolinite decreases by 18% and 24%, respectively. Then, to investigate the effect of clay minerals on contaminated soils, the shear resistance parameters of soil with kaolinite and soil with bentonite are compared. The results show, with variation of clay minerals in contaminated soils, resistance parameters have different behavior. Increasing the lead concentration in bentonite causes a flocculated structure, thus the shear strength increased. In soils with bentonite, shear strength parameters increase 20% to 30% with increasing the lead nitrate concentration