Abstract:

Aiming at the problem of ammonia-nitrogen wastewater pollution, walnut shell carbon was used as adsorbent, and the NH₄⁺ was used as model adsorption molecules. The effects of pretreatment conditions of walnut shell, roasting temperature, roasting time and initial concentration of ammonium ion on the adsorption of ammonia-nitrogen wastewater were investigated. The results showed that walnut shell carbon modified by H₃PO₄ (700℃, 2 h) had excellent adsorption capacity for low concentration NH₄⁺. When the initial concentration of NH₄⁺ was 0.8 mg/L, the amount of walnut shell carbon was 2 g/L and the adsorption time was 240 min, the adsorption rate was 93.41%. Adsorption of ammonium ion by walnut shell charcoal accorded with pseudo-second-order kinetics model. The specific surface area of the walnut shell carbon obtained by H₃PO₄ pretreatment was 269.18 m²/g, the total pore volume was 0.173 6 cm³/g, the micropore volume was 0.125 0 cm³/g and the average pore size was 5-46 nm. Phase characterization of walnut shell charcoal was carried out by infrared (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that walnut shell carbon modified by H₃PO₄ (700℃, 2 h) was graphite-carbon crystalline phase with graphite lamellar structure on its surface which resulted in good adsorption.

Key words: walnut shell carbon, ammonia-nitrogen ion, adsorption, wastewater