Abstract Conditional solubility of dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAp) in digester supernatant was determined as a function of pH and was compared to its conditional solubility in distilled water. Conditional solubility of both substances in digester supernatant at pH >5–6 was higher than their conditional solubility in pure water due to the presence of impurities, and this influence is more significant for HAp. Amorphous CaP was precipitated through a fast precipitation process from digester supernatant with initial total phosphate concentration 0.008 mol/L and 0.015 mol/L and Ca/P ratios 2 and 5. The amorphous CaP can be subsequently recrystallized into crystalline CaP. Obtained amorphous products have Ca/P ratio > 1, which allow performing the recrystallization process without further Ca dosing into the system. Batch recrystallization of the amorphous products resulted in crystallization of HAp, DCPD or their mixture depending on the conditions of the process. Maximum achieved P-recovery was 69.5%. The increase of phosphate concentration and the addition of seeding decreased the yield of the process but promoted crystallization of DCPD. The increase of Ca/P ratio had a positive effect on the total P-recovery. Compared with the direct batch crystallization of CaP from digester supernatant, the two-step process with fast precipitation and recrystallization significantly improved the color of the obtained products.

中文翻译：

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通过快速沉淀和重结晶从消化器上清液中回收磷酸钙

摘要 磷酸二钙二水合物 (DCPD) 和羟基磷灰石 (HAp) 在消化器上清液中的条件溶解度被确定为 pH 的函数，并与其在蒸馏水中的条件溶解度进行比较。由于杂质的存在，这两种物质在 pH > 5-6 的消化器上清液中的条件溶解度高于它们在纯水中的条件溶解度，并且这种影响对 HAp 更为显着。通过快速沉淀过程从消化池上清液中沉淀出无定形 CaP，初始总磷酸盐浓度为 0.008 mol/L 和 0.015 mol/L，Ca/P 比为 2 和 5。无定形 CaP 随后可以重结晶为结晶 CaP。获得的无定形产品的 Ca/P 比 > 1，这允许在不进一步向系统中加入 Ca 的情况下进行再结晶过程。取决于工艺条件，无定形产物的分批重结晶导致HAp、DCPD或它们的混合物的结晶。实现的最大 P 回收率为 69.5%。磷酸盐浓度的增加和晶种的加入降低了过程的产率，但促进了 DCPD 的结晶。Ca/P 比的增加对总磷回收率有积极影响。与从消化器上清液中直接分批结晶 CaP 相比，快速沉淀和重结晶的两步法显着改善了所得产品的颜色。磷酸盐浓度的增加和晶种的加入降低了过程的产率，但促进了 DCPD 的结晶。Ca/P 比的增加对总磷回收率有积极影响。与从消化器上清液中直接分批结晶 CaP 相比，快速沉淀和重结晶的两步法显着改善了所得产品的颜色。磷酸盐浓度的增加和晶种的加入降低了过程的产率，但促进了 DCPD 的结晶。Ca/P 比的增加对总磷回收率有积极影响。与从消化器上清液中直接分批结晶 CaP 相比，快速沉淀和重结晶的两步法显着改善了所得产品的颜色。