Investigation of sodium trapped by the filter cake during separation of iron from sewage sludge ash
Typ
Examensarbete för masterexamen
Program
Innovative and sustainable chemical engineering (MPISC), MSc
Publicerad
2021
Författare
Dahlbom Järvinen, My
Mäkitalo, Emmy
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The company EasyMining has developed a process, Ash2Phos, to recover P from
incinerated sewage sludge ash. The purpose of this report was to investigate the
cause of Na losses to the filter cake during separation of Fe in one of the process
steps. The project also aimed at exploring the influence of washing on the Na losses.
The investigation was done by conducting a process reproduction experiment on a
semi-pilot scale, including cycles with different washing conditions. Since the focus
of the project was the Fe separation step, the experimental setup was simplified
compared to the large scale process and did only include upstream process steps.
The evaluation of Na losses to the filter cake and the influence of washing were done
by constructing a mass balance, based on analyses with ICP-AES and ICP-MS,
over the process step for the cycles with different washing conditions. The evaluation
of the filter cake composition and elemental distribution was conducted by
SEM-EDS analysis on filter cakes with different washing conditions. Analysis with
XRD was also performed to investigate possible crystalline structures containing
Na. Additional experiments on lab scale were performed on one of the known filter
cake components, Al-silicates, to study its adsorption potential, washing behaviour
and influence on the Na losses. The studies identified three main Na containing
particles in the filter cake: Fe-precipitates, Al-silicates and Ca-precipitates. Extensive
washing was found to be efficient for Na removal from the filter cake, however,
only to a limited extent. Further, it was not possible to identify any crystalline
structures containing Na. Based on the lab scale experiment, the losses of Na to
the Al-silicates were not due to adsorption, instead it was related to trapped liquid
in the cake. Finally, Fe-precipitates were identified as the main contributors to the
Na losses but further studies are required to identify the mechanism and reduce the
losses. It would also be of great interest to optimise the washing by including a cost
perspective and large scale process conditions.
Beskrivning
Ämne/nyckelord
sodium losses , filter cake washing , adsorption of sodium , phosphorus recovery