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Bioremediation for Sustainable Environmental Cleanup

and

Figure 2.2. Factors influencing precipitation (Adapted from Yong et al. 2014).

Table 2.2. Kinetic Mechanisms of Precipitation (Adapted from Lewis 2017).

Kinetic Process

Definition

Impact on Precipitation

Nucleation

Creation of crystal particles occurring from

enlargement of ions or molecules in a supersaturated

state. Nucleation can be:

- Primary: spontaneous precipitation from solution

- Homogenous nucleation (spontaneous precipitation)

- Heterogeneous nucleation (prompted by foreign

particles)

- Secondary: prompted by the presence of existing

crystals

- Contact nucleation (via crystal-crystal contact)

- Shear nucleation (via fluid flow)

- Fracture nucleation (via particle impact)

- Attrition nucleation (via particle impact and

disruption)

High supersaturation → Primary nucleation

Low saturation → Secondary nucleation

Crystal Growth

Growth of crystal particles due to adsorption on

substance surfaces

High supersaturation → Rough crystals

Low saturation → Spiral or smooth crystals

High nucleation and low growth rate →

small but many crystals

Agglomeration

Enlargement of crystals due to prolonged contact and

formation of crystalline bridges between particles

High nucleation → many crystals → high

agglomeration

High agglomeration → Low crystal purity

treatment, chemical precipitation is applied through coagulation and flocculation, whereby the use

of a reagent is used to promote precipitation and aggregation, respectively (Davis 2010, Mihelcic

and Zimmerman 2014). Figure 2.2 demonstrates the various factors that affect precipitation and

potential impacts to its use as a remediation strategy. Of the factors identified, pH is the most

significant, whereby alkaline solutions tend to precipitate metal(loid)s and acidic solutions cause

dissolution of metal(loid) precipitates (Yong et al. 2014).