The hydrodynamics study was performed with Computational Flow Dynamics (CFD) tools which allow for the optimization of the operating conditions of the process, and to improve the velocity distribution and flow within the reactor, a computer with 8GB RAM and an AMD A8 was used.

This process the entrapment of the sulfates (SO₄⁼) by the aluminum hydroxide Al(OH)₃ was simulated which form flocs in an emulsion giving as product Al(OH)₃SO₄, These flocs subsequently sediment. To simulate this phenomenon, a three-phase Eulerian model was proposed for each substance involved in the process and an interaction between phases for a heterogeneous process and a drag coefficient between aluminum hydroxide and sulfates.

Introduction

Electrocoagulation (EC) is an electrochemical method which consists in situ generation of coagulants by electro-dissolution of aluminum electrodes. In this process, the generation of aluminum cations is carried out on the anode and hydrogen gas production on the cathode. This process generates aluminum hydroxides [1,2,3]. The principal reaction on the anode, the electro dissolution of aluminum generates aluminum ions (Al³⁺); therefore, the aluminum ions are transformed to aluminum hydroxides (Al(OH)_3(s)).

The sulfate removal mechanism by EC is carried through by adsorption in which aluminum hydroxides flocs entrap an SO₄^2- ion [2].

Results

Figure 1 shows the variation of sulfate concentration (CSO₄⁼) after the EC process as a function of the flow rate at the current density of 6 mA cm ^-2 constant for both the experimental and simulation phases. With respect to the experimental phase, the first section the CSO₄⁼ increases linearly between 1110 ≤ CSO₄⁼ ≤ 1650 mg L^-1 at 0.925 ≤ u ≤ 1.85 cms^-1. In the second section the CSO₄⁼ increases linearly between 1650≤ CSO₄⁼ ≤ 1900 mg L^-1 at 1.85 ≤ u ≤ 2.78 cms^-1 this may be due to the increase in linear velocity and for the third section, CSO₄⁼ again grow linearly between 1900 ≤ CSO₄⁼ ≤ 2100 mg L^-1 at 2.78 ≤ u ≤ 3.70 cms^-1.

For the initial concentration of 3500 mg L^-1 and the rate of 0.00925 ms^-1, sulfate was partially removed during EC from 3500 to 1110 mg L^-1 experimentally and for simulation was 3500 to 1000 mg L^-1 with a difference of removal between the experimental and the simulation of 4.71%. For the initial concentration of 3500 mg L^-1 and the rate of 0.0185 ms^-1, sulfate was partially removed during EC from 3500 to 1650 mg L^-1 experimentally and for simulation was from 3500 to 1720 mg L^-1 with a difference between the experimental and simulation removal 1.95%. For the initial concentration of 3500 mg L^-1 and the rate of 0.0278 ms^-1, sulfate was partially removed during EC from 3500 to 1900 mg L^-1 experimentally and for the simulation was 3500 to 2000 mg L^-1 with a difference of removal between the experimental and the simulation of 3.89%. For the initial concentration of 3500 mg L^-1 and the rate of 0.03703 ms^-1, the sulfate was partially removed during the EC from 3500 to 2100 mg L^-1 experimentally and for the simulation was from 3500 to 2150 mg L^-1 with a difference of removal between the experimental and the simulation of 0.70%.

Conclusions

A model computational fluid dynamic model for the hydrodynamic study showed that the flow remains in laminar regime throughout the process. It may be inferred that the reactor design presents suitable hydrodynamic conditions to operate in a range of inlet flow velocity of 0.00925 m/s to 0.037 m/s.

These results simulated compared to the experimental data indicate that the mass transfer (Eulerian) model is adequate to emulate the sulfate removal processes by means of electrocoagulation since the difference between the experimental and simulated data is in acceptable ranges to validate the theoretical model by means of the experimental results. And is observed that it is an efficient process in the cleaning sulfates of the mining effluents.

References

[1] Del Angel P., Carreño G., Nava J.; “Removal of Arsenic and Sulfates from an Abandoned Mine Drainage by Electrocoagulation. Influence of Hydrodynamic and Current Density”; Int. J. Electrochem. Sci., 9 (2014) 710 - 719

[2] Sandoval M. Nava J. Carreño G., Sulfate Ions Removal from an Aqueous Solution Modeled on an Abandoned Mine by Electrocoagulation Process with Recirculation, Int. J. Electrochem. Sci., 12 (2017) 1318 – 1330.

[3] Flores O.J., Nava J.L., Carreño G., Elorza E., Martinez F., 2013. Arsenic removal from groundwater by electrocoagulation in a pre-pilot continuous filter press reactor. Chemical Engineering Science, 97, 1-6.