Potassium fertilizers (potash) are mined in a handful of countries in the Northern Hemisphere. Potash is either expensive or unavailable to the farmers of the Southern Hemisphere. Alkaline alteration of K-feldspar rock (ultrapotassic syenite) in autoclave in the presence of Ca 2+ generates a mixture of K-bearing calcium-aluminum-silicate-hydrate (C-A-S-H) minerals that potentially can be used as an alternative local fertilizer. This work investigates the effect of processing temperature (200 °C, 220 °C, and 230 °C) and time (from 0.5 to 3.0 h) on pH, mineralogy, and elemental availability of the C-A-S-H mineral mixture. Increasing temperature results in an increased conversion of K-feldspar and increased content of both the mineral tobermorite (Ca 5 Si 6 O 16 (OH) 2 ·4H 2 O) and amorphous phase in the resulting C-A-S-H mixture; increasing time results in an increased conversion of α-dicalcium silicate hydrate into tobermorite. The amount of K leached from the mixture is relatively constant across all processing conditions. Hydrothermal alteration in autoclave of K-feldspar-bearing rocks such as ultrapotassic syenite permits the synthesis of a potential potassium fertilizer which alkalinity and mineralogy can be tailored according to soil requirements.

中文翻译：

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处理温度和时间对高压釜中钾长石岩石水热变​​化的影响

钾肥（钾肥）在北半球的少数几个国家开采。南半球的农民要么很贵，要么无法获得钾肥。在 Ca 2+ 存在下，高压釜中钾长石（超钾正长岩）的碱性蚀变产生含钾的钙铝硅酸盐水合物 (CASH) 矿物的混合物，该混合物有可能用作替代的当地肥料。这项工作研究了加工温度（200 °C、220 °C 和 230 °C）和时间（从 0.5 到 3.0 小时）对 CASH 矿物混合物的 pH 值、矿物学和元素可用性的影响。温度升高导致钾长石转化率增加，以及所得 CASH 混合物中矿物雪硅钙石（Ca 5 Si 6 O 16 (OH) 2 ·4H 2 O）和无定形相的含量增加；随着时间的增加，α-硅酸二钙水合物转化为雪硅钙石的转化率增加。从混合物中浸出的 K 量在所有加工条件下都相对恒定。高压釜中含钾长石的岩石（如超钾正长岩）的热液蚀变可以合成一种潜在的钾肥，其碱度和矿物学可以根据土壤要求进行调整。