Experimental Study Of Phosphorus Removal By Modified Pine Needles From Aqueous Solutions

Pine needles(PN) are the renewable resources with fast regeneration ability, and have a large amount of accumulation in the coniferous forests. Meanwhile, it can collect in all seasons. In this paper, raw PN and alkali-isopropanol pretreated PN could hardly decontaminate phosphorus from aqueous solutions in the phosphorus removal tests. Therefore, PN was modified chemically to improve the phosphorus removal efficiency. The influences of the initial phosphate concentration on pine needles(PN) and lanthanum-modified pine needles(LPN) adsorption was conducted and the result showed that PN barely remove phosphates from water solution at 25 ℃, while the maximum adsorption capacity of LPN was 4.80 mg P/g, and the maximum adsorption capacity APN was 0.98 mg P/g. Meanwhile, we studied the solution pH, temperature, coexisting ions and TOC of soluble organics and analyzed adsorption thermodynamic and kinetic parameters of phosphate removal by the modified pine needle removal. The results were listed as followings:When pH value was less than 3, it could promote the adsorption behavior and when the values of pH were between 3 and 9.5, the increasing of pH values showed little effect on phosphorus removal efficiency. The adsorption capacity of LPN and the phosphorus remvoal efficiency increased with the environmental temperature increasing. The value of ΔH° was 25.30 KJ/mol and it suggested that the removal of phosphate by LPN was an endothermic reaction. However, the value of ΔG ° decreased with ambient temperature rising. The results obtained from the experiments could be well fitted by the pseudo first order kenitic model, intraparticle diffusion model, the pseudo seconf order kenitic model, Langmuir and Freundlich models. The analysis of the intra-particle diffusion model suggested boundary layer adsorption affected it slightly and intra-particle diffusion dominated the adsorption process. No significantly competitive behavior between other co-existing anions and phosphorus was observed. However, when the concentrations of carbonate anions were higher than >50 mg/L, the competive effect of carbonate were exhibited and the efficiency of phosphorus remvoal decreased. Alkali-isopropanol pretreatment and La-modification could significantly reduce the releasing of organic compounds. The porous structure of the inner profile of LPN was also observed in the SEM pictures, that maybe due to the extraction of organic matters of PN tissues by isopropanol which result in a larger specific surface area and easier for attachment of lanthanum hydroxide.This article briefly described the recovery technology, electrolysis, crystallization, adsorption/desorption, biochar recycling and soil system recovery technology, analyzed the feasibility of biomass materials and elaborated prospects of phosphorus recovery.