Characteristics of amine-crosslinked wheat straw and its adsorption mechanisms for phosphate and chromium (VI) removal from aqueous solution

A new adsorbent was prepared from wheat straw (WS) after the crosslinking of amine groups. Its adsorption characteristics and operating parameters for phosphate and chromium (VI) removal were studied. BET surface area, elemental content and zeta potential analysis illustrated the physicochemical change between amine-crosslinked wheat straw (AC-WS) and WS. Significant variation in Raman shift of phosphate/chromium (VI)-loaded AC-WS was observed, and the results suggested the differential adsorption mechanisms for phosphate and chromate (VI) removal by AC-WS. The adverse effect of ionic strength on phosphate and chromate (VI) uptake suggests the possibility of ion exchange mechanisms being active in the adsorption process. The regeneration capacities for phosphate-loaded AC-WS and chromium (VI)-loaded AC-WS were 98.1% and 74.8%, respectively, which validated a potential chemical bonding between chromium (VI) and AC-WS. In addition, the adsorption capacities of AC-WS for phosphate and chromate (VI) were 1.71 and 5.68 mmol/g, respectively, providing a potential application of AC-WS for toxic heavy metals and nutrient substances removal from aqueous solutions.