This paper presents a case study of the use of a non-intrusive passive acoustic sensor for on-line monitoring of flow and related process parameters. The sensor was mounted externally on a small diameter pipeline conveying dense slurries of fine silica particles. Origins of the acoustic emissions in the pipeline are discussed, particularly, with reference to interactions with flow parameters of interest in process control. The statistical and spectral characteristics of the collected acoustic signal for different experimental conditions were utilized to build quantitative models to infer parameters such as solid concentration, volume flowrate and mass flowrate. The results indicate that passive acoustic signals can be a viable tool for on-line monitoring of slurry flows.