Effects of phosphate and citric acid on Pb adsorption by red soil colloids

Abstract

There are abundant organic acids in rhizospheric soil, which may interfere in the reaction between phosphate and heavy metals. Effects of phosphate on Pb2+ adsorption by red soil colloids(Ultisol) were studied in the presence of citric acid (Cit) through batch equilibrium experiments, Zeta potential and X‐ray diffraction (XRD) analyses. Results showed that in the presence of different concentrations of phosphate (P), the peak‐like curves of Pb2+ sorption was moved up even disappeared. When the Langmuir equation was used to model isothermal adsorption curve of Pb2+, the adsorption reaction constant (K), the maximum adsorption quantity (Xm) of several treatments were both in a decreasing order of 1.0 mmol/L P > 1.0 mmol/L P + 0.5 mmol/L Cit > 0.5 mmol/L Cit. Under the influence of citric acid, the Pb2+ adsorption amount increased at pH < 4.5, and then decreased gradually with pH increase. The order of Zeta potential reduction was: 1 mmol/L P + 0.5 mmol/L Cit > 0.5 mmol/L Cit > 1 mmol/L P, which were different from that of the Pb2+ adsorption amount, suggesting that the adsorption of Pb2+ was not only an electrical adsorption in the presence of P. XRD patterns proved that occurrence of pyromorphite for the treatment with 1.0 mmol/L P addition, whereas no lead phosphate peak was detected in other treatments. The mechanism of Pb2+ adsorbed in red soil colloids with addition of phosphate was primary formation of pyromorphite‐like compounds. However, 0.5 mmol/L Cit inhibited the formation of pyromorphite. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 969–974, 2016

Sorption of Pb(II) and Cu(II) on the colloid of black soil, red soil and fine powder kaolinite: effects of pH, ionic strength and organic matter

“…The changes in pH cause a remarkable change of the sorption of Pb(II), and it is similar to the observation published earlier for the sorption of hydrolysable metal ions [22]. Besides, the increasing pH value might accelerate the hydrolysis of Pb(II), and the formed hydroxyl ion was easier to be adsorbed by soil colloids [23]. The adsorption on RS and KL have the same change tendency.…”

Reduction of Cd accumulation in pak choi (Brassica chinensis L.) in consecutive growing seasons using mercapto-grafted palygorskite

“… 36 Phosphate added to red soil decreased the soil zeta potential, while net negative charges on the surface increased, leading to the enhancement of Pb 2+ electrostatic adsorption. 43 The addition of MP enhanced the sorption of bioavailable Cd to soil, which could be a remediation mechanism of MP.…”

A Freundlich‐type multi‐component approach for modeling the sorption of nickel and phosphate in soil

“…A simpler approach to describing the sorption of various solutes by soils is via the use of empirical sorption isotherms. For example, Freundlich and Langmuir isotherms have been used to describe the increased sorption of metal cations in the presence of phosphate, and vice versa (Li et al, 2006;Ren et al, 2012Ren et al, , 2015Selim et al, 2013;Stietiya & Wang, 2014;Zhao & Selim, 2010;Zuo et al, 2016). However, a limitation to these isotherms is that parameters are unique to specific experimental conditions.…”

“…Previous studies demonstrated an increase in the sorption of phosphate by soils in the presence of Zn (Pérez-Novo et al, 2011b) as well as by ferrihydrite in the presence of Zn (Liu et al, 2016) and Cd (Liu et al, 2018); however, increased phosphate sorption by soils in the presence of Ni has not been reported previously. The increased sorption of heavy metal cations in the presence of phosphate, and vice versa, has been attributed to electrostatic effects (Antelo et al, 2015;Collins et al, 1999;Venema et al, 1997), the formation of Type A and Type B ternary surface complexes (Elzinga & Kretzschmar, 2013;Liu et al, 2016Liu et al, , 2018Swedlund et al, 2009;Tiberg & Gustafsson, 2016;Tiberg et al, 2013), and coprecipitation (Stietiya & Wang, 2014;Zuo et al, 2016). However, speciation calculations using MINTEQ 3.1 indicate that solution concentrations of Ni and P phosphate were well below saturation for any Niphosphate precipitate, so coprecipitation was unlikely.…”