Fly ashes heated at temperatures ranging from 600°C to 1, 600°C were reacted at 80°C for 4 hrs and then at 180°C for 24 hrs at fly ash-CaO-CaSO₄·2H₂O-water ratio by weight 100 : 20 : 5 : 1, 250. For each preparation, unreacted fly ash, change of mineral composition of fly ash before and after the reactions, and solubilities of SiO₂, Al₂O₃, Na₂O and K₂O from fly ash were determined.
The following are clarified from these experiments :
(1) When fly ash was heated at 1, 000°C, the content of glass phase was decreased and that of mullite was increased. Besides, cristobalite and anorthite were newly formed. At 1, 300°C, the vitrification proceeded to dissolve α-quartz and minor crystalline components. At 1, 600°C, even mullite was completely dissolved to give only a glass phase.
(2) The crystallization of fly ash accelerated the formation of ettringite and C-S-H at the reaction at 80°C, and that of 11Å tobermorite at 180°C. On the contrary, the vitrification of fly ash tended to facilitate the formation of monosulphate at 80°C, and hydrogarnet at 180°C.
(3) The crystallization of fly ash resulted in the decrease of Al₂O₃ content due to the increase of mullite and formation of anorthite and relative increase of Na₂O and K₂O content in the glass phase.
These changes improve the reactivity of crystallized fly ash and accelerate the formation of 11Å tobermorite rather than hydrogarnet.

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Fine grain dicalcium phosphate anhydride (DCP) was prepared by an effervescing reaction between calcium carbonate and phosphoric acid. Calcium carbonate powder was added by vigorously stirring into phosphoric acid (0.05-10 mol%) until the pH of the solution had risen to 2.5 at a temperature from 10 to 60°C. The DCP crystals obtained were 0.5-3.9 μm in size. The particle size decreased with higher concentrations of phosphoric acid and lower temperatures of the reaction. The CDP contained a small amount of water from the results of DTA and TG.

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Tests were made on removal of phosphate ions such as H₂PO₂^- and HPO₃^2- in plating waste solutions by the Yatugatake volcanic ash soils.
The sedimentation characteristics of the soil particles were also studied.
The following results were obtained;
1) The recycle method was useful to remove the phosphates at a high efficiency.
2) The simple sedimentation rate of the ash soils was 5.4mm/min.
The agglomerative sedimentation rate with PA-377 was 40 times larger, indicating that the latter method was efficient.
3) The agglomerative sedimentation rate was influenced by pH and species of the ions. In the H₃PO₂ solutions, the sedimentation behavior was good at pH of 5.0, 7.0 and 9.0 but in the H₃PO₃ system, the sedimentation occurred only at pH value of around 5.0.

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Homogeneous precipitation method using urea was applied to the preparation of calcium phosphates. Acidic-aqueous solutions (0.5 mol·dm^-3 HNO₃ 500cm³) containing 0.167 mol·dm^-3 Ca (NO₃) ₂, 0.1 mol·dm^-3 (NH₄) ₂HPO₄ (Ca/P=1.67) and 0.5 mol·dm^-3 (NH₂) ₂CO were refluxed respectively at 80, 90, 95 and 100 °C for various lengths of time. The pH of each solution was measured continuously during the reaction. The products were characterized by X-ray powder diffractometry, IR spectroscopy, SEM and TG. During the reaction, two morphologies of the products were formed and separated into two layers at the initial stage; agglomerates of particles of dicalcium phosphate anhydrate (CaHPO₄) at the bottom of the flask and fibrous octacalcium phosphate [Ca₈H₂ (PO₄) ₆·5H₂O, OCP] in the upper solution. After the reaction finished, both products changed completely into apatite containing CO₃^2- (CO₃Ap).
The other results were as follows :
(1) A mixture of whisker-like CO₃Ap and fibrous CO₃Ap was obtained under the reaction conditions of 100°C-17h and 95°C-47h and 90°C-80h, the fibrous OCP was also obtained at 80°C-22h. The CO₃Ap was formed with the hydrolysis of CaHPO₄ and OCP, which both precipitated at the initial stage.
(2) By heating up to 1200°C in air, the CO₃Ap obtained at 95°C-47h and 90°C-80h changed into hydroxyapatite [Ca₁₀ (PO₄) ₆ (OH) ₂, HAp], losing CO₂. The CO₃Ap obtained at 100°C-17h changed into the mixture of HAp and α-tricalcium phosphate [α-Ca₃ (PO₄) ₂, α-TCP] by heating. Even after the heating, the HAp had whisker-like or fibrous morphology. However, the OCP fiber shrank and showed partially sinterability due to the heating.
(3) The flexible sheets and porous compacts of CO₃Ap and OCP were obtained.

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Experimental results about the dissolution of sparingly soluble substance with strongly acidic ion exchange resin, H-form (H-R), has been reported in order to clarify the dissolution mechanism.
The unique method has some following advantages :
a) Dissolution progress can be followed as a function of pH and specific conductivity (k) accompanied by the cation exchange reaction.
b) Because of absence of foreign ion due to other mineral acid, greater precision in chemical analysis will be expected.
The paper deals with a qualititative analysis of dissolution process during dropwise addition of H-R suspension by measuring the variations in pH and k.
The results obtained are summarized as follows;
1) Both BaSO₄ and CaC₂O₄·H₂O dissolve readily to split off the constitutional sulfate and oxalate ions, respectively, while the dissolution of calcium phosphate compound proceeds in two stages giving Ca (H₂PO₄) ₂ as an intermediate product for HAp or TCP.
2) Alkaline earth carbonate (MCO₃) also dissolves in two stages, but undergoes an unexpected reaction. Initial dissolution process accompanied with a remarkable increase in k value at pH≅7 can be explained by the following equation to yield the bicarbonate compound,
2MCO₃ + 2 (H-R) → M-R₂ + M (HCO₃) ₂… (1)
and followed by the successive exchange reaction,
M (HCO₃) ₂ + 2 (H-R) → M-R₂ + 2H₂O + 2CO₂… (2)

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