Green and cost-efficient functionalized clay adsorbent enables one-step ultraefficient removal of Pb(II) at very low and high concentrations

Abstract

It is always a huge challenge to purify wastewater containing very low or high concentrations of heavy metal ions to drinking water level (World Health Organization (WHO) guidelines) by one-step static or dynamic adsorption with a highly efficient, cost-effective, and environmentally friendly adsorbent. In response to this challenge, a green, low cost and powerful porous silicate/Fe3O4 adsorbent (named MCSiMg49) with ultra-strong purification ability towards the Pb(II) in both low- and high-concentration wastewater was developed using natural abundant, safe, and nontoxic palygorskite-rich clay as the starting material and water as the only solvent. The adsorbent possesses a high specific surface area of 332.41 m2/g (2.81 times that of raw clay), and was proven to be the best one to date that can purify deeply Pb(II) in water. The adsorption capacity of the adsorbent towards Pb(II) reached 499.3 mg/g, and 99.8% of Pb(II) can be removed from 800 mg/L Pb(II) solution after adsorption with 3 g/L of the adsorbent, which is significantly superior to other adsorbents and commercial activated carbon (AC). The adsorption column packed with MCSiMg49 (1 g, upper layer) and clay (1 g, lower layer) can remove completely Pb(II) from natural water (e.g., Yangtze River water or Yellow River water) (concentration: 50 mg/L), and 3000 mL clean drinking water (WHO guidelines) was obtained by a one-step filtration process. The MCSiMg49 adsorbent is easy to use in both dynamic and static adsorption, because it can be quickly recycled from the solution by external magnetic field after use. The adsorption of Pb(II) on the adsorbent was mainly driven by the cooperation of electrostatic attraction, ion exchange, chemical complexation and in situ mineralization of Pb(II).