Dear, it depends on what you have to model. For sure if you have to model an uniform mud flow you should use a non Newtonian model for the material, such as Herschel-Bulkley. Regarding the solver, if you have multiple phases, I suggest interFoam or interDyMFoam if your mesh is deforming (for example if you have rigid floating objects).

Franco

Keep me updated plz.

Franco

I believe ANSYS has a good power of dealing with such case studies, including full CFD, chemical treatment, and associated elctro-physics simulations..etc.

For example, see https://www.ansys.com/en-gb/solutions/solutions-by-industry/materials-and-chemical-processing/water-and-wastewater