Characteristics of phosphate-ion adsorption on N-doped activated carbon derived from pinecones and urea

Anion exchange resins are widely used to remove phosphate from water, but they have problems such as high costs and difficulty in reuse. In this study, we attempted to increase the quaternary nitrogen (N-Q) in activated carbon by impregnating pinecone with urea and zinc chloride and activating them at 600°C to improve the adsorption performance of phosphate ion. The sample using a mixture of pinecone, urea, and zinc chloride in a weight ratio of 1:4:1, which is Ur4-1, achieved the highest amount of 0.29 mmol/g for phosphate adsorption. Additionally, as the weight ratio of urea in the raw materials rose, the amount of N-Q of the samples showed an increasing tendency, whereas the specific surface area of the samples showed a decreasing tendency. This result suggests that the effect of N-Q content of the samples on phosphate ion adsorption performance is greater than that of specific surface area, which is a general indicator of the adsorption capacity of activated carbon. Ur4-1, which contained the largest amount of 1.81 wt% N-Q in this study and had good phosphate ion adsorption performance, was investigated for the amount of phosphate ion adsorption at equilibrium pH (pHe) 2-10. As a result, the amount of phosphate ion adsorption for Ur4-1 was 0.051 mmol/g higher than that of commercial anion exchange resin, IMAC HP555, at pHe 3.