Predicting breakthrough of vanadium in fixed-bed absorbent columns with complex groundwater chemistries: A multi-component granular ferric hydroxide−vanadate−arsenate−phosphate−silicic acid system

Abstract

Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater chemistries. The BTCs were simulated successfully using a homogeneous surface diffusion model (HSDM) combining equilibrium chemical adsorption and kinetic mass transfer. Adsorption parameters for various groundwater compositions were predicted using the CD-MUSIC surface complexation model, which was set up for the first time for akaganéite-based granular ferric hydroxide with a competitive multi-solute system. The results indicated that V(V) is less prone to competitive adsorption effects, and use of the homogeneous surface diffusion model to predict the BTCs requires then the kinetic mass transfer Biot number to be used as the only fitting parameter. On the other hand, a concentration overshoot could be observed for the two weaker absorbed oxo-anions arsenate and phosphate because of displacement by the vanadate. Results of pilot scale test column BTCs of vanadate for three waterworks with different groundwater compositions could be favorably extrapolated with a unique Freundlich constant k F of 3.2 derived on basis of the multi-solute CD-MUSIC model, and a unique Biot number of 37 fixed for all three different test sites.

Pre‐deposited dynamic membrane adsorber formed of microscale conventional iron oxide‐based adsorbents to remove arsenic from water: application study and mathematical modeling

“…A mathematical model incorporating the HSDM has been applied to describe the concentration profiles of arsenic adsorption systems, 8,58–61 These studies have demonstrated that the HSDM allows the simulation of the dynamic behavior of a variety of adsorbates (phosphate, arsenic, chloroform and vanadium) onto porous adsorbents (e.g. activated carbon, GFH and μGFH), as long as the mass transfer from the solution to the adsorption sites within the adsorbent particles is constrained by mass transfer resistances such as surface diffusion and external film mass transfer, as depicted in Fig.…”

“…It has been proven that the mathematical model based on the HSDM has the capacity to describe the impact of water chemistry (e.g. pH and water matrix) on adsorbate dynamic behavior if the adsorption equilibrium and kinetic parameters under changed water quality conditions are available (have been derived) 60,61 . This software (FAST 2.1) provides a numerical solution of Eqns (1) and (2) to simulate the concentration profile of anions over time of a fixed‐bed adsorption filter packed with an adsorbent used in water treatment.…”

Predicting the Breakthrough of Ternary Ca–Uranyl–Carbonate Species in Mineral Water Treated by a Fixed-Bed Granular Ferric Hydroxide Adsorbent

“…The effective surface diffusion coefficient gave distinct nonlinear intragranular adsorbate concentration gradients, as found by electron probe microanalysis of grains used to sorb vanadium. 14 Other assumptions incorporated into the HSDM approach were (i) that the hydraulic load rate and advective plug−flow conditions in the adsorbent bed (H in the HSDM) were constant, (ii) that solid phase mass transfer occurred through surface diffusion (SD in the HSDM), (iii) that linear aqueous phase mass transfer occurred through film diffusion, (iv) that the solute inflow concentrations were constant, (v) that the adsorbent grains were spherical, and (vi) that nonlinear (Freundlich or Langmuir) isotherms were used to describe the adsorption equilibrium. 17 The adsorbent bed used in the column experiments was characterized using bed length l, radius r, particle density ρ P , mean particle diameter d P , bed density ρ B , bed porosity ε B , adsorbent mass m A , and adsorbent bed volume BV.…”

“…In early attempts, BTCs were fitted using Gompertz sigmoid functions, but the polynomial curves produced by these functions have no physical or chemical meaning and therefore cannot be used to investigate systematically the effects of key parameter interference on breakthrough, such as the effects of changes in the pH and phosphate, silicate, and arsenate co-adsorbate concentrations reported on vanadate breakthrough. 14 Key factors that affect U(VI) breakthrough have not yet been investigated in a systematic way. However, from our current understanding of U(VI) complexation chemistry in groundwater involving ternary Ca uranyl carbonato complexes, and the strong effects of these complexations on U(VI) adsorption by ferric hydroxides, we hypothesize that elevated carbonate oxyanion and Ca concentrations typical of mineral water can strongly affect U(VI) breakthrough in FBAs containing GFH adsorbents.…”

“…However, it has been found that effects on vanadate BTCs for GFH can be successfully predicted using a homogeneous surface diffusion model (HSDM) involving an explicit simulation of mass transfer terms and adsorption kinetics, and that adsorption equilibrium can be predicted using a surface complexation model (SCM). 14 This is because the SCM parameters are, unlike adsorption isotherms, independent of experimental conditions. Our main hypothesis was that it may be possible to use this approach to investigate U(VI) sorption.…”