Sol-Gel Processes in Micro-Environments of Black Shale: Learning from the Industrial Production of Nanometer-Sized TiO2 Polymorphs
- Resource Type
- article
- Authors
- Hans-Martin Schulz
- Source
- ChemEngineering, Vol 3, Iss 1, p 28 (2019)
- Subject
- black shale
brookite
micro-environment
sol-gel process
Chemistry
QD1-999
- Language
- English
- ISSN
- 2305-7084
Micro-environments in black shale are reactors for geochemical reactions that differ from the bulk scale. They occur in small isolated pores of several 10 s to 100 s of nanometers without or with limited ionic exchange by diffusion to the surrounding matrix. The example of the formation of titania polymorphs brookite (and anatase) in black shale demonstrates that pH < 4 of the pore waters or lower must prevail to enable dissolution of Ti-bearing precursors followed by the precipitation of these metastable solids. Comparably low pH is applied during the industrial production of nanometer-sized brookite or anatase by sol-gel methods. The process parameters during industrial production such as low pH, negative Eh, or low ionic strength (to promote agglomeration) allow a comparison with parameters during geochemical processes leading to titania formation in black shale. Sol-gel processes are suggested herein as key geochemical processes in micro-environments of black shale in order to understand the formation of single brookite crystals or agglomerates on a nanometer scale.