*Article* **An Improved Evaluation Strategy for Ash Analysis Using Scanning Electron Microscope Automated Mineralogy**

#### **Andrea C. Guhl 1, Valentin-G. Greb 1, Bernhard Schulz 2 and Martin Bertau 1,\***


Received: 31 March 2020; Accepted: 20 May 2020; Published: 25 May 2020

**Abstract:** Sewage slush ashes are materials composed of polyphase particles. Ashes are fine-grained with many amorphous components, and analytical techniques such as X-ray diffractometry cannot recover all the properties. For sewage sludge ash, treatment often focuses on phosphate recovery. Automated mineralogy techniques were applied in order to study phosphate associations and their behavior towards chemical processes. This work shows the distribution of phosphate content in sewage sludge ash and identifies the main recovered phosphate phases in acid leaching. Data interpretation was focused on the target material, phosphate. The approach documents spectra labelling with respect to one target component, phosphorus. This is a tool for assessing sewage sludge ashes towards their phosphate recovery potential and highlights issues processing needs to address.

**Keywords:** sewage sludge ashes (SSA); phosphate; recycling; recovery; SEM-automated mineralogy; mineral liberation analysis (MLA)
