Application of Hydrodynamics Using CFD in Evaluating Efficacy of External Loop Air-lift Reactor Biochemical Leaching of Sea Nodules

ABSTRACT

Biochemical leaching of sea nodules using Bacillus circulans was carried in an external circulation-loop airlift bioreactor. In contrast to the slightly high recovery (92% Cu, 73% Ni, 72% Co, 38% Mn, and 17% Fe) with fine particles (<75 µm) on shake flasks in 25d, the leaching of metals using coarser lumps (1190–250 µm size fraction) were found to be 76% Cu, 69% Ni, 65% Co, 29% Mn and 12% Fe in the same duration in an air-lift reactor with airflow of 500L min⁻¹. The use of air flow assisted in retaining good metal recoveries with reduced grinding costs in the air lift reactor. Computational Fluid Dynamics (CFD) with a multiphase mixture model was used to describe the mass transfer and hydrodynamics vis-à-vis its role in improved leaching efficacy. The leach liquor was treated to eliminate iron, followed by selective extraction of copper by 10% Acorga M5640. The remaining leach liquor with Mn, Co and Ni were separated as respective salts by sulfide/carbonate precipitation.

KEYWORDS:

• Sea nodules
• biochemical leaching
• air-lift reactor
• CFD modeling
• separation

Nomenclature

General symbols	=
$d_b$ Diameter of the bubbles (m)	=
d (=1 mm) is external draft tube diameter	=
g Gravitational acceleration (m s−2)	=
k Turbulence kinetic energy of specific phase (m2 s−2)	=
p Pressure (Pa)	=
t Time (s)	=
$F_m$ Body force	=
$M_m$ Influence of the surface tension force on the mixture	=
$\overrightarrow{\underset{mN}{v}}$ Diffusion velocity	=
$\overrightarrow{v_N}$ Volume flow rate of the phase N per unit cross-section of flow area	=
$\overrightarrow{V_N}$ Actual velocity of the phase N	=
Ksp Solubility product	=
Greek symbols	=
α Phase volume fraction	=
β Molecular viscosity (Pa s−1)	=
${\mu }_{t,m}$ Mixture turbulent viscosity	=
${\mu }_{l,m}$ Mixture molecular viscosity	=
$\prime {{\sigma }_l}^{\prime }$ Is water superficial tension (N m−1)	=
${\tau }_m$ Average viscous stress	=
${\tau }_{\delta m}$ Average turbulent stresses*	=
Subscripts	=
N Phase	=

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work was supported by the Council of Scientific and Industrial Research [OLP111].