Experimentally and spectroscopically evidenced mechanistic study of butyl peroxyacid oxidative degradation of benzo[a]pyrene in soil.

Benzo[a]pyrene (BaP) is a major indicator of soil contamination and categorized as a highly persistent, carcinogenic, and mutagenic polycyclic aromatic hydrocarbon. An advanced peroxyacid oxidation process was developed to reduce soil pollution caused by BaP originating from creosote spills from railroad sleepers. The pH, organic matter, particle size distribution of soil, and concentrations of BaP and heavy metals (Cd, Cu, Zn, Pb, and As) in the BaP-contaminated soils were estimated. A batch experiment was conducted to determine the effects of organic acid type, soil particle size, stirring speed, and reaction time on the peroxyacid oxidation of BaP in the soil samples. Additionally, the effect of the organic acid concentration on the peroxyacid degradation of BaP was investigated using an oxidizing agent in spiked soil with and without hydrogen peroxide. The results of the oxidation process indicated that BaP and heavy metal residuals were below acceptable Korean standards. A significant difference in the oxidative degradation of BaP was observed between the spiked and natural soil samples. The formation of a peroxyacid intermediate was primarily responsible for the enhanced BaP oxidation. Further, butyric acid could be reused thrice without losing the efficacy (<90%). The systematic peroxyacid oxidative degradation mechanism of BaP was also discussed. A qualitative analysis of the by-products of the BaP reaction was conducted, and their corresponding toxicities were determined for possible field applications. The findings conclude that the developed peroxyacid oxidation method has potential applications in the treatment of BaP-contaminated soils.

Oxidation of sulphide in abandoned mine tailings by ferrate.

In this study, Fe(VI) was applied to treat three mine tailings containing different amounts of sulphides and heavy metals. Oxidation of sulphides by Fe(VI) was studied at pH 9.2 with variation of solid to solution ratio, Fe(VI) concentration and injection number of Fe(VI) solution. The major dissolved products from the treatment of mine tailings with Fe(VI) solution were sulphate and arsenic. Oxidation efficiency of sulphides was evaluated by reduction efficiency of Fe(VI) as well as by measurement of dissolved sulphate concentration. Even though inorganic composition of three mine tailings was different, reduction fraction of Fe(VI) was quite similar. This result can suggest that Fe(VI) was involved in several other reactions in addition to oxidation of sulphides. Oxidation of sulphides in mine tailing was greatly dependent on the total amount of sulphides as well as kinds of sulphides complexed with metals. Over the five consecutive injections of Fe(VI) solution, dissolved sulphate concentration was greatly decreased by each injection and no more dissolved sulphate was observed at the fifth injection. While dissolved arsenic was decreased lineally up to the fifth injection. Sulphate generation was slightly increased for all mine tailings as Fe(VI) concentration was increased; however, enhancement of oxidation efficiency of sulphides was not directly proportional to the initial Fe(VI) concentration.

Phosphorus removal using cow bone in hydroxyapatite crystallization.

The applicability of cow bone as a seed material in hydroxyapatite crystallization was investigated in this research. Seed crystal used for the experiments was prepared by the calcination of cow bone. The effects of initial calcium concentration, pH, alkalinity, reaction temperature condition, and calcination temperature were examined for synthetic solution by batch experiment. The experimental results showed that a good phosphorus removal could be achieved by cow bone crystal seeding. The phosphorus removal rate with various calcium concentrations and pHs could be predicted from high relationships between residual phosphorus concentration and pH (after reaction). The effects of alkalinity, reaction temperature condition, and calcination temperature were also examined by rate constant analysis.