بررسی اثر ترکیب نانوذرات سیلیکا و سیمان بر تثبیت خاک رس آلوده به فلز سنگین نیکل

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی عمران، دانشگاه آزاد اسلامی واحد همدان، همدان، ایران

چکیده

چکیده: هدف از این مطالعه بررسی توانایی ترکیب سیمان- نانو سیلیکا (CNS) در افزایش بهره‌وری فرآیند تثبیت و جامدسازی (S/S) خاک‌های آلوده به فلزات سنگین است. به این منظور، ابتدا رس کائولینیت در شرایط آزمایشگاه به فلزنیکل آلوده و سپس با انجام مجموعه ای از آزمایش‌های مختلف، تاثیر استفاده از ترکیب CNS در پاکسازی خاک ارزیابی شد. نتایج بدست آمده مؤید آن است که در مصالح رسی حاوی فلز سنگین با شرایط کانی ساخت مشابه کائولینیت، امکان تراوش آلودگی حتی در غلظت‌های کم آلاینده (10cmol/kg.soil<) وجود دارد و نیازمند تدابیر لازم برای پاکسازی است. افزودن سیمان به کائولینیت، قابلیت نگهداشت فلز سنگین را به شدت افزایش داده، اگر چه آزمایش TCLP نشان داد آبشویی این نمونه ها نیز سبب بازگشت مجدد تا 30% آلاینده جذب شده به سیال منفذی می‌گردد. هم‌چنین مشخص شد اندرکنش سیمان با فلز نیکل، فرآیند جامدشدگی ذرات را مختل کرده که در نتیجه ی آن، بهبود مشخصات ژئومکانیکی خاک تا 4 برابر کاهش می یابد. مشاهده شد CNS در مقایسه با سیمان، حدود 60% از توانایی بیشتری در غیرمتحرک‌سازی آلاینده برخوردار است و ضمن افزایش 40 درصدی مقاومت فشاری، تا دو برابر قابلیت فشردگی مصالح را کمتر می‌کند. براساس نتایج حاصل از آزمایش های فیزیکی-مکانیکی، طیف های XRD و تصاویر SEM، علت عملکرد بهتر ترکیب CNS ناشی از رشد بیشتر (به طور متوسط حدود 42 درصد) و سریعتر مواد سیمانی (خصوصااً ژل CSH)، کاهش اثر مخرب تشکیل رسوب فلز سنگین بر واکنش‌های هیدراتاسیون و افزایش تراکم ساختار ارزیابی شد. در مجموع یافته های پژوهش حاضر نشان می دهد با مدنظر قراردادن ضوابط EPA، حدود 0/5 سیمان به ازای هر سانتی مول بر کیلوگرم غلظت نیکل و حدود یک ماه نگهداری، برای پاکسازی ایمن خاک لازم است که در حضور نانو ذرات سیلیکا، مصرف سیمان (تا 35%) و زمان عمل آوری ( تا سه برابر) کاهش خواهد یافت.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Effect of SiO2 Nanoparticles and Cement on the Performance of Stabilized Ni-Contaminated Clayey Soils

نویسندگان [English]

  • A. R. Goodarzi
  • M. Zamanian
Faculty of Engineering, Hamedan Branch, Islamic Azad University, Hamedan, Iran
چکیده [English]

This study investigates the capability of cement-SiO2 nanoparticles (CNS) mixture to the promotion of stabilization/solidification (S/S) process of heavy metal (HM) contaminated soils. For this purpose, artificially contaminated soil samples were first prepared by mixing kaolinite with nickel (Ni) and then a set of tests were performed to assess the effectiveness of the CNS treatment. The results indicate that the addition of cement markedly increases the HM retention of soil; however, the TCLP tests show that leaching of cement treated samples leads to return a part of pollutants to soil pore fluid. The cement and Ni interaction has a destructive impact on particles solidification which adversely affects the strength development and compressibility of the cement-stabilized specimens. At same condition, the CNS blend is more efficient in immobilizing Ni and modifying the soil engineering properties as compared to sole cement. Based on the physicochemical, XRD and SEM tests, the better performance of CNS agent is mainly associated with the more and faster growth of cement compounds, reducing the adverse effect of heavy metal precipitation on the hydration reactions and increasing the particle density. The study concluded that with the consideration of EPA criteria, an optimum cement content of 0.5 wt% per one cmol/kg.soil of HM within 28 days of curing can successfully remediate the Ni contaminated soils. The incorporation of SiO2 nanoparticles into the binder system improves the microstructure and geomechanical performance of stabilized materials and causes a significant reduction in the cement consumption (up to 35%) and time of curing (up to 3 times)

کلیدواژه‌ها [English]

  • Remediation of Heavy Metal Contaminated Soil
  • Cement
  • SiO2 Nanoparticles
  • Improvement of Microstructure
  • Promotion of S/S process

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نشریه مهندسی عمران امیرکبیر
دوره 49، شماره 4
اسفند 1396
صفحه 821-830

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