Summary

This chapter covered suspension density, crystal size and the amount of fine crystals as the characteristics affecting the filtration ability. In the case of changing suspension density, essentially low suspension density increased α_c and decreased filtration rate.

Especially α_c increased exponentially around 0.5g/L. Moreover focused on crystal size, the range which changed α_c exponentially moved to higher suspension density by sieving operation. Meanwhile α_c increased with additive ratio of fractured crystals. But in the 50% condition, α_c decreased because of the dissolution of fractured crystals.

84 References

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Conclusion

The present thesis is researched the relationships between filtration abilities and crystal abilities. Especially filtration abilities of cake filtration which targeted crystal products were investigated from the view point of the crystallization process. The thesis is constructed mainly three part, one is the reaction crystallization chapter. It discussed about controlling carbonate crystallization with reaction crystallization (crystal size, shape, dispersity). In the reaction crystallization chapter, calcium, lithium and strontium carbonate crystals were selected to the target carbonates, and single-jet system was applied to the performance. From the previous study on a carboxyl containing polyelectrolyte effect, PAA (viz. PolyAcrylic Acid) was additive to the reaction field to control size, shape and dispersity. And obtained crystals were used to the filtration study.

The filtration research has two parts from main three part of construction. One is the focused on crystal abilities like crystal size, shape, applied to carbonate crystals for standard sample from previous chapter. And one is the focused on actually industrial process, MAP crystallization which were applied to phosphate recovery system. The main discussion of the present study is summarized as follows: (a) study on operation conditions with carbonates reaction crystallization. Especially feeding condition which affected supersaturation rate, reaction time which affected to the crystal growth, reaction agent concentration which affected to the supersaturation were investigated (b) study on PAA effects for carbonate crystallization. PAA improve the crystal products quality for example downsizing, mono-dispersity, inhibition of agglomeration was investigated (c) research of filtration abilities (e.g. filtration resistance, filtration volume) with crystal abilities applied to the carbonate crystals. Changed the carbonate crystals condition, constant pressure filtration experiments were performed and discussed about effects given by crystals characteristics. (d) research of filtration abilities about MAP crystallization. Especially be conscious with actually industrial process,

Chapter 1 introduced fundamental information of crystallization and solid-liquid separation especially filtration. And the relationships of them were discussed.

Especially polyelectrolyte effects and method to organized filtration abilities information were core part. Crystal products often produced in micro to millimeter order, so microfiltration is suitable to solid-liquid separation for suspension solution.

And then, filter pore size is too small comparison with crystals, cake filtration model is corresponded to the system. Ruth equation is considered to the best method to discuss filtration abilities.

Chapter 2, which located in a core topic of through the thesis, discussed about carbonate and MAP reaction crystallization and polyelectrolyte effect on them. First, various operation conditions leads various condition crystals. But non-additive reaction field has envelope, polyelectrolyte was applied to the systems. PAA was the most effective polymer for the carbonate crystallization and crystals were improved on size, controlled shape, inhibited agglomeration. Combined with results of operation conditions like feeding rate, and polyelectrolyte effects were shown additional new results.

Chapter 3 demonstrated filtration experiment applied with previous results which obtained crystals in chapter 2. Micro filtration was performed on various condition carbonate crystals and filtration abilities were discussed. The case of different shape and same chemical compounds, filtration abilities affected by crystal shape and cubic or sphere shape of crystals increased filtration resistance in larger size areas than needle shapes. And another result, when the breakdown of crystals were happened, renewed fine crystals were birth, and increased filtration resistance regardless of measured crystal size.

Chapter 4 demonstrated filtration experiment of MAP crystallization. Especially, be conscious to the actually industrial systems, mainly suspension density and/or crystal size effects were focused. As a result, suspension conditions were very important factor for filtration. Small suspension density increased the filtration resistance because of the difference of style the sedimentation. Low suspension density formed tight cake layer sedimentation. And fine particle attachment to the other crystals was affected to the filtration resistance. There is fine crystals ratio which waited for constant time, attached fine crystals each other and apparent crystal size was increased, filtration resistance was decreased.

A series of the discussions proposes next step of polyelectrolyte effects on reaction crystallization and research of new discipline of filtration discussions.