Crystallization by particle attachment (CPA) is the non-classical process whereby solids grow by stepwise addition and attachment of particles ranging from multi-ion complexes to nanoparticles. Developing a comprehensive, quantitative understanding of CPA will deepen our understanding of many low-temperature mineral-forming processes, as well as provide insights into novel synthesis methods for technological applications. However, this potential cannot be fully realized without new information on the specific steps involved in CPA, as well as how those steps are connected.
Current knowledge gaps are due to the lack of experimental methodologies for making direct, real-time observations of CPA processes in solution. Furthermore, much research is still based on samples synthesized at randomly chosen (ad hoc) conditions, which are often not representative of that found in nature. Few studies have taken a fully systematic approach to characterizing the structure and composition of both the precursors (monomers, multi-ion complexes and nanoparticles) and final solids as a function of synthesis (formation) conditions. Furthermore, it is not clear how the aggregation of particles that leads to CPA is affected by hydrodynamic conditions, and how this fits into existing theoretical models of particle-particle interactions and aggregation behavior used extensively in water treatment technologies.
New systematic and real-time approaches to study CPA are needed to produce quantitative, self-consistent models of (nano)mineral formation in low-temperature aqueous conditions. These new models will not only lead to a more thorough understanding of the biogeochemical cycling of nutrients/metals, but will also help develop better strategies for environmental remediation.