Enhancing irrigation water quality efficiently with potassium feldspar-derived adsorbent: Heavy metal detoxification...

The pollution of Pb²⁺ and Cd²⁺ in both irrigation water and soil, coupled with the scarcity of vital mineral nutrition, poses a significant hazard to the security and quality of agricultural products. An economical potassium feldspar-derived adsorbent (PFDA) was synthesized using potassium feldspar as the main raw material through ball milling-thermal activation technology to solve this problem. The synthesis process is cost-effective and the resulting adsorbent demonstrates high efficiency in removing Pb²⁺ and Cd²⁺ from water. The removal process is endothermic, spontaneous, and stochastic, and follows the quasi-second-order kinetics, intraparticle diffusion, and Langmuir model. The adsorption and elimination of Pb²⁺ and Cd²⁺ is largely dependent on monolayer chemical sorption. The maximum removal capacity of PFDA for Pb²⁺ and Cd²⁺ at room temperature is 417 and 56.3 mg·g^-1, respectively, which is superior to most mineral-based adsorbents. The desorption of Pb²⁺/Cd²⁺ on PFDA is highly challenging at pH≥3, whereas PFDA and Pb²⁺/Cd²⁺ are recyclable at pH≤0.5. When Pb²⁺ and Cd²⁺ coexisted, Pb²⁺ was preferentially removed by PFDA. In the case of single adsorption, Pb²⁺ was mainly adsorbed onto PFDA as Pb₂SiO₄, PbSiO₃·xH₂O, Pb₃SiO₅, PbAl₂O₄, PbAl₂SiO₆, PbAl₂Si₂O₈, Pb₂SO₅, and PbSO₄, whereas Cd²⁺ was primarily adsorbed as CdSiO₃, Cd₂SiO₄, and Cd₃Al₂Si₃O₁₂. After the complex adsorption, the main products were PbSiO₃·xH₂O, PbAl₂Si₂O₈, Pb₂SiO₄, Pb₄Al₂Si₂O₁₁, Pb₅SiO₇, PbSO₄, CdSiO₃, and Cd₃Al₂Si₃O₁₂. The forms of mineral nutrients in single and complex adsorption were different. The main mechanisms by which PFDA removed Pb²⁺ and Cd²⁺ were chemical precipitation, complexation, electrostatic attraction, and ion exchange. In irrigation water, the elimination efficiencies of Pb²⁺ and Cd²⁺ by PFDA within 10 min were 96.0 % and 70.3 %, respectively, and the concentrations of K⁺, Si⁴⁺, Ca²⁺, and Mg²⁺ increased by 14.0 %, 12.4 %, 55.7 %, and 878 %, respectively, within 60 min. PFDA holds great potential to replace costly methods for treating heavy metal pollution and nutrient deficiency in irrigation water, offering a sustainable, cost-effective solution and paving a new way for the comprehensive utilization of potassium feldspar.