Enhancement of Solid Dissolution by Ultrasound
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Alternative Energy Forms & Transfer Mechanisms (AE)
Keywords: Dissolution, Sphalerite concentrate, Ultrasound, Variable effect, Kinetic modelling
Acoustic cavitation is an emerging option for enhancing physical and chemical processes. The effects of ultrasound include cleaning, degassing and enhancement of mass transfer coefficient as well as reactions yield.
We investigated the ultrasonic enhancement of the reduction of dissolved ferric iron (Fe3+) to ferrous iron (Fe2+) with sphalerite (zinc sulphide) concentrate in a sulphuric acid solution, which is an industrially important reaction in zinc production:
Fe2(SO4)3(aq) + ZnS(s) ↔ 2FeSO4(aq) + ZnSO4(aq) + S(s)
The experiments were performed in a 1000 ml stirred glass reactor, which was placed in a water bath made of stainless steel. To this bath, six 30 kHz ultrasound transmitters with a variable maximum effect of 50W were coupled. An edged heating plate with silicon oil was used for temperature control. The reactor was equipped with a pitched-blade turbine, an oil lock, baffles and a reflux condenser.
The temperature of the experiments varied between 75-95°C. The initial concentration of ferric iron was 0.179 mol/l and an equimolar amount i.e. 1:2 reducing agent-to-ferric iron molar ratio was used in a 0.40 M sulphuric acid solution. The total amount of the liquid was 750 ml. The stirring rate was varied between 200 and 700 rpm. The effect of ultrasonic power, duration of ultrasound cycles and the time between the cycles were studied. The concentration of ferric iron was determined by sequential injection analysis (SIA) and SEM pictures were taken to determine the shape and size of the solid particles.
The apparent effect of ultrasound varied depending on the conditions used, but it clearly enhanced both the rate and yield of the reaction especially when the impact of mass transfer was essential.
Eleven different models were tested for silent systems [H. Markus et al. 2004]. These models are utilized in the present kinetic study for explaining the kinetics of the reduction reaction of spherical particles when ultrasound is employed.
Presented Wednesday 19, 11:00 to 11:20, in session EPIC-1: Alternative Energy Forms & Transfer Mechanisms (AE).
