Adsorption of Phosphonate Antiscalant HEDP from Reverse Osmosis Concentrates by La/FeOOH@PAC

doi:10.15541/jim20200512

Abstract

Abstract:

Phosphonate antiscalants are commonly used in reverse osmosis (RO) membrane desalination to prevent fouling by mineral scale. However, due to its adverse effects on the ecosystem and the removal of hardness from RO concentrates, it is necessary to remove phosphonate antiscalants before RO concentrates disposal. In this work, using powder activated carbon (PAC) as carrier, La/FeOOH@PAC composite material was prepared via co-precipitation of lanthanum hydroxide and iron oxyhydroxide. The synergistic effect of La/Fe enhanced the adsorption capability of the composite material. Morphology and structure of the adsorbents were characterized by different methods. Adsorption behavior and properties of this composites for phosphonate antiscalant 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) in simulated reverse osmosis concentrates were also investigated. The effect of molar ratio of La to Fe, adsorption time, initial concentration of HEDP and temperature on the adsorption performance were investigated in details. The results showed that La/FeOOH@PAC composites was successfully synthesized by co-precipitation method. Under the adsorption conditions of 298 K, pH=8.0 and dosage of 0.4 g·L^-1, the adsorption isothermal was in accordance with the Langmuir model, and the theoretical maximum adsorption capacity was 65.359 mg·g^-1. Its adsorption kinetics could be fitted well with the pseudo-second-order kinetics equation, and adsorption behavior was an exothermic and spontaneous process. XPS analysis showed that the main adsorption mechanism of the adsorbent was the ligand exchange between hydroxyl groups linked with La/Fe and HEDP.

Key words: iron oxyhydroxide, lanthanum, powder activated carbon, HEDP, antiscalant

CLC Number:

O647

LI Chuang, YANG Qingfeng, LU Shengsen, LIU Yangqiao. Adsorption of Phosphonate Antiscalant HEDP from Reverse Osmosis Concentrates by La/FeOOH@PAC[J]. Journal of Inorganic Materials, 2021, 36(8): 841-846.

Figures/Tables 12

Table 1 Simulation solution of RO concentrates

Concentration/(mg·L^-1)							T/K	Initial pH
HEDP	Ca²⁺	Mg²⁺	Na⁺	Cl^-	SO₄^2-	HCO^-	T/K	Initial pH
18.00	298	8.00	204.54	397.86	407.62	542.46	298	8.00

Fig. 1 Variation of HEDP adsorption capacity on La/FeOOH@PAC with different molar ratios of the La/Fe Absorbent dosage: 0.4 g/L, Absorption time: 12 h

Fig. 2 XRD patterns of PAC and La/FeOOH@PAC

Fig. 3 Different magnification FE-SEM images of La/FeOOH@PAC composite

Table 2 Elemental composition of the adsorbent

Element	C	O	Fe	La
wt%	86.27	12.04	1.05	0.64

Fig. 4 Adsorption kinetics of HEDP onto the adsorbent

Table 3 Parameters of kinetic models for HEDP adsorption onto the La/FeOOH@PAC composite

T/K	Q_e,exp/(mg·g^-1)	Pseudo-first-order equation			Pseudo-second-order equation
T/K	Q_e,exp/(mg·g^-1)	k₁/h^-1	Q_e/(mg·g^-1)	R²	k₂/(g·mg^-1·h^-1)	Q_e/(mg·g^-1)	R²
298	41.600	0.476	24.143	0.983	0.0659	42.553	0.999

Fig. 5 Adsorption isotherm of HEDP onto the adsorbent

Table 4 Parameters of isotherm models for HEDP adsorption onto the adsorbent

T/K	Langmuir model parameters			Freundlich model parameters
T/K	Q_m/ (mg·g^-1)	K_L/ (L·mg^-1)	R²	n	K_F	R²
298	65.359	0.455	0.974	1.880	19.249	0.864
308	56.818	0.674	0.992	2.446	21.509	0.949
318	56.689	0.512	0.993	2.211	18.571	0.940

Fig. 6 Linear plots fit of lnKd versus Cefor the adsorption HEDP onto the adsorbent at different temperatures (a); linear plots of lnK0 versus 1/T for the adsorption of HEDP onto the adsorbent (b)

Table 5 Thermodynamic parameters for HEDP adsorption onto the adsorbent

T/K	ΔG^o/(kJ·mol^-1)	ΔH^o/(kJ·mol^-1)	ΔS^o/(J·mol^-1 K^-1)
298	-7.579	-9.632	-6.834
308	-7.567
318	-7.440

Fig. 7 Wide scan (a), P2p (b) and O1s (c, d) XPS spectra of the adsorbent before and after adsorption

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