Removal of Pb2+ and Cd2+ from irrigation water and replenishment of mineral nutrients using a low-cost mineral adsorbent derived from potassium-rich aluminum silicates

Abstract

Heavy metal pollution and a lack of essential mineral nutrients in irrigation water seriously impact crop safety and quality. A low-cost mineral adsorbent (LCMA) was created using mechanochemical methods from illite, wollastonite, gypsum, dolomite, and calcium carbonate (molar ratio of 2:1:1:3:9) to remove Pb2+ and Cd2+ and supplement mineral nutrients in irrigation water. The results showed that LCMA had a higher removal capacity than most similar mineral materials, with maximum adsorption capacities of 278 and 83.1 mg·g–1 (298 K) for Pb2+ and Cd2+, respectively. At pH ≥ 3, there was very little Pb2+ and Cd2+ desorption from LCMA, whereas desorption was simple at pH ≤ 0.5, indicating the chemical stability of LCMA. Pb2+ and Cd2+ are competitive adsorptions, with Pb2+ taking precedence. In actual irrigation water, the removal rates of Pb2+ and Cd2+ by LCMA were approximately 90 % and 80 %, respectively, within 10 min. Complexation and co-precipitation were used to attach Pb2+ and Cd2+ to LCMA, followed by ion exchange and electrostatic interaction. Pb2+ was primarily adsorbed on LCMA as PbAl2O4, Pb2SiO4, and PbSO4, whereas Cd2+ was primarily adsorbed as Cd3Al2Si3O12 and CdSiO3. In addition, with the application of LCMA, the concentrations of Si4+, K+, Ca2+, and Mg2+ in the polluted irrigation water increased by 12.4 %, 22.8 %, 78.9 %, and 439 %, respectively. LCMA is a strong candidate to replace the current expensive remediation technology for heavy metal pollution and lacking mineral nutrients in irrigation water.