بررسي استفاده از مواد معدني و الكتروسينتيك چرخشي در افزايش مقاومت فشاري بتن و تاثير آن در تثبيت و جامدسازي سرب، روي، و آرسنيك

EFFECT OF INORGANIC MATERIAL AND NON-UNIFORM ELECTROKINETIC ON SOLIDIFICATION/STABILIZATION OF LEAD, ZINC AND ARSENIC

در اين مطالعه، براي بررسي تاثير و بهينه‌سازي 6 متغير: نسبت وزني خاكستر بادي (1X)، رس اسيدي (2X)، ميكروسيليس (3X) به سيمان، نسبت آب به مواد جامد (4X)، ولتاژ اعمالي (5X)، و دوره‌ي تعويض قطبيت ميدان الكتريكي (6X) در الكتروسينتيك چرخشي در تثبيت و جامدسازي پسماند مصنوعي حاوي سرب، روي، و آرسنيك از روش سطح پاسخ و طرح مركب مركزي استفاده شده است. بر روي 86 نمونه‌ي آزمايشگاهي ساخته‌شده، آزمايش مقاومت فشاري و تعيين pH و بر روي نمونه‌هاي با بيشينه و كمينه‌ي مقاومت فشاري، آزمايش TCLP و عكس‌برداري الكتروني (SEM) انجام شده است. نتايج نشان داده است كه به‌علت حضور گسترده‌ي 8AH2C، 10CAH، كلسيم سيليكات هيدراته، محصورشدن آرسنيك در O2H5/7.4NaCaAsO، و روي و سرب در كريستال‌هاي پرتلنيت، كاهش ذرات سيمان غيرهيدراته و اترينگايت در شرايط بهينه، ميزان مقاومت فشاري، pH نمونه، غلظت سرب، روي و آرسنيك در شيرابه‌ي TCLP، به‌ترتيب برابر Mpa56/57، 82/9، mg/L4/0، mg/L393/0، و mg/L146/0 بوده است.

In this study, the effects of fly ash (X1), kaolinitic clay (X2), micro-silica (X3) content and water-to-solid ratio (X4), electrical potential gradient (X5) and polarity reversal period (X6) on the solidification and stabilization of Synthetic waste containing lead, zinc and arsenic were investigated. The data were analyzed using the central composite design which is the most commonly used response surface methodology RSM design (using a mixture design of a constrained triangular surface) and ANOVA. Optimum formulations were simulated using a desirability function. pH and compressive strength tests were performed on 86 specimens. The specimens with the highest and lowest compressive strengths were selected for Toxicity characteristics leaching procedure (TCLP) and scanning electron microscopy (SEM) to evaluate the leaching behavior of lead, zinc and arsenic and monitoring hydration progress, respectively. The experiments were arranged according to a full factorial design, which also allowed deriving predictive models for unconfined compressive strength and pH as affected by Synthetic waste content as well as variables type and dosage. Among the variables tested, polarity reversal period (less than 32.5min) and micro-silica (more than 7.5 % wt.) were found to affect mechanical strength far more positively compared to the other species used, at the same time ensuring low metal release from the material. On the other hand, the use of polarity reversal period more than 32.5 min and micro-silica less than 7.5% wt. were observed to cause a significant increase in metal leaching. The result indicates that the extensive accumulations of calcium aluminate hydrates (CAH) which are the main products of tri-calcium aluminate (C3A) and calcium silicate hydrate (CSH) were identified as the main hydration products. The formation of NaCaAsO4•7.5H2O and portlandite were the main phase controlling As5+ and heavy metal solubility in cement-treated Synthetic wastes. The optimal conditions obtained from the compromise of the two desirable responses, pH and compressive strength of specimens, were lead, zinc and arsenic concentration in TCLP leachate 0.4 mg/L, 0.393 mg/L and 0.146 mg/L, respectively. pH and compressive strength of specimens in the optimal condition were 57.56 Mpa and 9.82, respectively