**3.3 Lepidocrocite (γ-FeOOH)**

Lepidocrocite precipitated at lower temperatures than magnetite. By using NaCl solutions of 5M and temperature of 40°C, the morphology of the crystals formed was affected by the pH. Plates crystallized at pH 5.5, rods at pH 7, and multi-domain crystals at pH 8.2 (**Figure 10**). The difference between the morphologies results from faster crystallization of 010 along c direction in crystals formed at higher pH leading to multi-domain crystals at pH 8.2. Similar results were also obtained at 25°C [13].

#### **Figure 7.**

*Pictures obtained by HRSEM presenting the morphology of magnetite crystals precipitated at salinity of 4 and 5M NaCl, pH 9.4, and temperature of 60–80°C.*

#### **Figure 8.**

*Pictures obtained by HRSEM presenting the morphology of magnetite crystals precipitated at salinity of 4 and 5M NaCl, pH 10, and temperature of 60–70°C.*

**99**

**Figure 11.**

**3.4 Effect of additional Si**

Addition of Na2SiO3H2O into the solutions was selected to see the effect of Si on iron oxide crystallization. In precipitation of magnetite crystals, Na2SiO3H2O was added to a solution of 4M NaCl, pH 7.5 at a temperature of 60°C. The presence of Si

*Pictures obtained by HRTEM presenting the effect of additional Na2SiO3H2O to solution of 4M NaCl, at 40°C.*

*Goethite crystals observed through HRTEM. The crystals were synthesized at 40°C, in solutions of 2 and 5M* 

*Lepidocrocite crystals observed through TEM. Crystals were formed in NaCl solutions of 5M concentration at 40°C and pH 5.5, 7, and 8.2. At pH 8.2 magnetite crystals co-precipitated with multi-domain lepidocrocite.*

*Iron Oxides Synthesized in Hypersaline Solutions DOI: http://dx.doi.org/10.5772/intechopen.88948*

*NaCl and with additional NaHCO3 or at pH 8.2.*

**Figure 9.**

**Figure 10.**

*Iron Oxides Synthesized in Hypersaline Solutions DOI: http://dx.doi.org/10.5772/intechopen.88948*

#### **Figure 9.**

*Mineralogy - Significance and Applications*

**98**

**Figure 8.**

**Figure 7.**

*5M NaCl, pH 9.4, and temperature of 60–80°C.*

*5M NaCl, pH 10, and temperature of 60–70°C.*

*Pictures obtained by HRSEM presenting the morphology of magnetite crystals precipitated at salinity of 4 and* 

*Pictures obtained by HRSEM presenting the morphology of magnetite crystals precipitated at salinity of 4 and* 

*Goethite crystals observed through HRTEM. The crystals were synthesized at 40°C, in solutions of 2 and 5M NaCl and with additional NaHCO3 or at pH 8.2.*

#### **Figure 10.**

*Lepidocrocite crystals observed through TEM. Crystals were formed in NaCl solutions of 5M concentration at 40°C and pH 5.5, 7, and 8.2. At pH 8.2 magnetite crystals co-precipitated with multi-domain lepidocrocite.*

**Figure 11.** *Pictures obtained by HRTEM presenting the effect of additional Na2SiO3H2O to solution of 4M NaCl, at 40°C.*
