Composite washing of cadmium (Cd)- and lead (Pb)-contaminated agricultural soil from Hunan province in China using mixtures of chlorides (FeCl 3 , CaCl 2 ) and citric acid (CA) was investigated. The concentrations of composite washing agents for metal removal were optimized. Sequential extraction was conducted to study the changes in metal fractions after soil washing. The removal of two metals at optimum concentration was reached. Using FeCl 3 mixed with CA, 44 % of Cd and 23 % of Pb were removed, and 49 and 32 % by CaCl 2 mixed with CA, respectively. The mechanism of composite washing was postulated. A mixture of chlorides and CA enhanced metal extraction from soil through the formation of metal–chloride and metal–citrate complexes. CA in extract solutions promoted the formation of metal–chloride complexes and reduced the solution pH. Composite washing reduced Cd and Pb in Fe–Mn oxide forms significantly. Chlorides and CA exerted a synergistic effect on metal extraction during composite washing.
Aihua Qiao,Yanyi Duan,Xue Gao,Ning Ren,Renliang Huang,Jiangjiexing Wu,Wei Qi,Anastasia Penkova,Rongxin Su
Oil from offshore oil spills may be stranded on beaches and exist for decades, requiring appropriate cleaning agents to adequately remove it. Herein, a phosphorylated cellulose nanocrystals (PCNCs) −Tween80 composite cleaning agent was developed by adding trace amounts of nonionic surfactant Tween80. Through the synergistic interaction of various components, the cleaning agent exhibited high oil removal efficiencies for the oiled sand at 25 ℃ and sea salt concentration of 3.5 wt%. The difference among the oil removal efficiencies of cleaning agents containing different components was mainly attributed to variations in the interfacial tension and the zeta potential. The oil removal efficiencies of the cleaning agent for contaminated sand containing engine oil were 81.2 % and 91.4 % at the cleaning speeds of 150 rpm and 300 rpm, respectively. Surprisingly, the composite cleaning agent reached an oil removal efficiency of 89.9 % at just 150 rpm for the real-world polluted system of the sand contaminated with crude oil. At a relatively mild cleaning speed of 150 rpm, the cleaning effect exceeded those reported in most previous studies at 300 rpm. Furthermore, the washing wastewater achieved rapid and efficient oil/water separation under flocculation of using polyaluminum chloride, which was expected to significantly reduce the discharge of wastewater and avoid secondary pollution. This work has developed a PCNCs-based cleaning agent with advantages of high efficiency, environment-friendliness, convenient preparation, low cost, and low discharge of wastewater, which can efficiently remove oil from oiled sand.
危险品化学品经营许可证（带存储）