**1. Introduction**

In 2014, the European Commission published a document on critical raw materials, including phosphate [1]. In conjunction with the circular economy initiative of the European Commission, the waste managemen<sup>t</sup> sector started working on commodity recovery from materials previously regarded as disposable. Thereby, the term "resources" was widened from ores to include industrial ashes. Several countries are incinerating sewage sludge, as previous disposal choices are no longer an option legally [2]. The resulting sewage sludge ash (SSA) is now the product workers are focusing P-recovery techniques on (e.g., [3–8]). SSA is not only complex in composition, but also diverse (depending on provenance, incineration parameters and other factors). In order to optimize recovery techniques, the P-content (target) needs exploring. Here, strategies from primary resources may help. This paper follows previous work [9–11] and adds insights from scanning electron microscopy-based automated mineralogy (SEM-AM) work, a technique from primary resources, to this waste managemen<sup>t</sup> issue. A number of systems are available among this group, such as QEMSCAN, Mineralogic, TIMA (TESCAN Integrated Mineral Analyzer) and MLA (Mineral Liberation Analyzer).

Knowing both particle morphology as well as composition is an advantage in devising technologies to extract a targeted component from a diverse material. Addressing these issues, the MLA by FEI, Inc. was chosen to study SSA particles with an SEM-AM system [12]. This offers a complete phase analysis (definitive array of minerals), as well as information about the X-ray amorphous components. Since current approaches to evaluating these datasets aim at identifying minerals among the EDX spectra [13–15], and SSA do not consist of known minerals only, the evaluation of datasets needed some adjustments [16]. Here, we present an approach to complex material investigation using SEM-MLA.

#### **2. Materials and Methods**
