Solar-driven hydrothermal gasification is an efficient process to exploit the energetic potential of biomass containing high amounts of water. This process requires effective removal of the type-2 salts from the feedstock as their precipitates can plug the equipment and poison the gasification catalyst. This work investigates the effect of the axial temperature profile on type-2 salt deposition in a dip-tube salt separator operated with an aqueous Na2SO4 solution as model feed and presents a method for online detection and monitoring of the growth of the deposits. Our results suggest that preventing the salt deposition at the wall of the separator by controlling the axial temperature profile is not possible. The online monitoring of the salt deposition is thus indispensable for scheduling the timely removal of the salt deposits.