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

Takaaki Wajima

doi:10.3390/pr8111484

Abstract

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.

Highlights

In oil-fired power plants, oil-fired fly ash following discharge, prior to passing through a flue, is collected by cyclones or electrostatic precipitators
Because oil-fired fly ashes have a high content of vanadium (V) and nickel (Ni), their recovery from heavy oil ash has attracted attention since the 1960s worldwide [1]
S-impregnated carbonaceous adsorbents with high heavy metal removal were prepared from an industrial waste—paper sludge—by pyrolysis after immersion in potassium sulfide (K2 S) solution [13]

Summary

Introduction

In oil-fired power plants, oil-fired fly ash following discharge, prior to passing through a flue, is collected by cyclones or electrostatic precipitators. The produced unburned carbon (carbonaceous residues) from the ash has to be disposed of to landfill sites, requiring high processing costs [3] Because they have a high carbon content and heavy metal-free, these residues can be used as precursors for activated carbon [4,5,6] or be burned with or without coal in a coal boiler for energy recovery. Processes 2020, 8, 1484 pollutants from aqueous solutions, because of its relatively nonpolar character [7] This property prevents the attraction between some functional groups on activated carbon surface and charged metal species. S-impregnated carbonaceous adsorbents with high heavy metal removal were prepared from an industrial waste—paper sludge—by pyrolysis after immersion in potassium sulfide (K2 S) solution [13]. To clarify the effect of S in the raw ash, the adsorbent was prepared by the same procedure using potassium hydroxide (KOH) solution to compare the properties of lead removal

Heavy Oil Ash

Preparation of Adsorbent

Characterization

Results and Discussion

Lead removal abilities of Product-K

Isotherm ofoflead