نوع مقاله: علمی - پژوهشی

نویسندگان

1 کارشناسی ارشد فرآوری مواد معدنی، دانشگاه بیرجند، بیرجند، ایران

2 استادیار گروه مهندسی معدن، دانشکده مهندسی، دانشگاه بیرجند، بیرجند، ایران

چکیده

پساب‌های حاصل از برخی فعالیت‌های معدنکاری و متالورژیکی حاوی مقدار قابل توجهی سیانید هستند که بواسطه سمیت بالای سیانید باید قبل از ورود به محیط ‌زیست تصفیه شوند. یکی از تکنولوژی‌های کاربردی برای حذف سیانید از پساب، روش جذب سطحی است. هیدروکسیدهای دوگانه لایه‌ای (LDH) گروه خاصی از کانی‌های رسی بوده که با موفقیت برای حذف برخی آلاینده‌های آنیونی از محلول‌های آبی بکار گرفته شده-اند. در این تحقیق LDH با استفاده از فرآیند هم‌رسوبی و نسبت 3:1 از نمک‌های نیترات منیزیم و آلومینیوم با خلوص آزمایشگاهی و صنعتی سنتز گردید و کاربرد آن برای حذف سیانید (CN-) از محلول‌های آبی مطالعه شد. ترکیب شیمیایی و کانی شناسی نمونه سنتز شده توسط XRD، XRF، میکروسکوپ الکترونی روبشی (SEM) و طیف‌سنج تفکیک طول موج (WDX) بررسی شدند. تأثیر پارامترهای دما، جرم جاذب، سرعت همزن و pH بر ظرفیت جذب LDH به روش طراحی آزمایش با استفاده از نرم افزار DX7 بررسی شد. شرایط بهینه جهت حذف یون سیانید در دمای oC60، جرم جاذب 5/1 گرم، دور همزن rpm500 و pH برابر با 52/9 تعیین گردید که در این شرایط بیشترین میزان ظرفیت جذب LDH سنتز شده برای سیانید به میزان mg/g 80/73 به دست آمد. داده‌های ظرفیت تعادلی از مدل لانگمیر و داده‌های سینتیک جذب از مدل سینتیکی شبه مرتبه دوم به بهترین وجه پیروی می‌کند. مرحله کنترل کننده نرخ جذب براساس انطباق داده‌های جذب با مدل وبر و موریس، نفوذ درون‌ذره‌ای تشخیص داده شد و نحوه جذب یون سیانید بر LDH با توجه به ترکیب شیمیایی و ساختار کانی‌شناسی آن از نوع تبادل یونی است. LDH سنتز شده با استفاده از نمک‌های با خلوص صنعتی نیز قابلیت بالایی برای حذف یون سیانید از محلول نشان داد. همچنین تصفیه پساب واقعی توسط LDH نشان داد که با دوز جاذب g/L20 می‌توان بیش از 84% سیانید را از پساب حذف نمود.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

The study of the removal conditions of free cyanide from wastewaters by layered double hydroxide through experimental design technique, kinetic and equilibrium studies

نویسندگان [English]

  • Rasool Alaei 1
  • sepideh javanshir 2
  • Ali Behnamfard 2

1 M.Sc. student of mineral processing engineering, Faculty of Engineering, University of Birjand, Birjand, Iran

2 Mining engineering department, Faculty of Engineering, University of Birjand, Birjand, Iran.

چکیده [English]

The wastewaters of the mining and metallurgical activities must be treated before discharging into the environment due to the highly toxicity of cyanide. One of the most efficient technologies for the removal of cyanide from wastewaters is adsorption. In this research, layered double hydroxides (LDHs) known as anionic clays was synthesized by co-precipitation process using a 3:1 ratio of magnesium nitrate and aluminum nitrate and used for removal of cyanide from aqueous solutions. The chemical and mineralogical compositions of LDH were investigated using XRD, XRF and Scanning Electron Microscopy (SEM) and Wavelength Dispersive X-ray (WDX) analysis methods. The largest particle size of LDH was determined about 4 nm using Scherrer equation which indicates that the synthesized LDH is in the range of nano-sized materials. The effect of temperature, absorbent dosage, stirring speed and pH on the adsorption capacity of LDH for cyanide was investigated using experimental design method by DX7 software. The optimum conditions were determined to be temperature=60oC, adsorbent weight=1.5 g, rotation speed=500 rpm and pH=9.52. In this condition, the maximum adsorption capacity of synthesized LDH for cyanide was 73.80 mg/g. The equilibrium data and the kinetic data were best modeled by Langmuir isotherm model and pseudo-second-order kinetic model, respectively. The rate limiting step was determined to be intraparticle by adopting the adsorption data with Weber and Morris model and the adsorption of cyanide onto LDH is occurred through ion-exchange mechanism due to chemical composition and mineralogical structure of LDH. LDH synthesized using salts of industrial purity also showed high potential for removal of cyanide ions from the solution. Also, the treatment of a real wastewater by LDH showed that with an absorbent dose of 20 g /L, more than 84% of the cyanide can be removed from the wastewater.

کلیدواژه‌ها [English]

  • Cyanide contaminated wastewater
  • Layered Double Hydroxide
  • Adsorption
  • Design of experiment
  • Kinetic and equilibrium Modeling

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