Carbonaceous Adsorbent Derived from Sulfur-Impregnated Heavy Oil Ash and Its Lead Removal Ability from Aqueous Solution

• Main Author: Takaaki Wajima
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Processes
• Subjects: heavy oil ash; K₂S immerse; pyrolysis; lead removal; selectivity
• Online Access: https://www.mdpi.com/2227-9717/8/11/1484

A novel carbonaceous adsorbent was prepared from sulfur-impregnated heavy oil ash via pyrolysis using potassium sulfide (K₂S) solution, and its ability to remove lead (Pb²⁺) from aqueous solutions was examined. It was compared with an adsorbent synthesized by conventional pyrolysis using potassium hydroxide (KOH) solution. Specifically, the raw ash was immersed in 1 M K₂S solution or 1 M KOH solution for 1 day and subsequently heated at 100–1000 °C in a nitrogen (N₂) atmosphere. After heating for 1 h, the solid was naturally cooled in N₂ atmosphere, and subsequently washed and dried to yield the product. Regardless of the pyrolysis temperature, the product generated using K₂S (Product-K₂S) has a higher sulfur content than that obtained using KOH (Product-KOH). Moreover, Product-K₂S has a higher lead removal ability than Product-KOH, whereas the specific surface area of the former is smaller than that of the latter. Product-K₂S obtained at 300 °C (Product-K₂S-300) achieves the highest lead adsorption and a high selective lead removal from a ternary Pb²⁺–Cu²⁺–Zn²⁺ solution. The equilibrium capacity of Product-K₂S-300 was found to fit the Langmuir model better than the Freundlich model, and its calculated maximum adsorption capacity is 0.54 mmol/g. From the ternary Pb²⁺–Cu²⁺–Zn²⁺ solution, the order of adsorption by Product-K₂S-300 is Pb²⁺ > Cu²⁺ > Zn²⁺, and the removal of Pb²⁺ and Cu²⁺ increases as the pH of the solution increases.