Effect of sintering temperature of potassium feldspar‐limestone/dolomite on composition and microstructure of silicate fertilizers

Acid soils call for a fertilizer providing base cations (Ca, Mg, K, et al.) and releasing nutrients with a gradual rate. The dissolution rate from soil minerals such as potassium feldspar ( KA lSi 3 O 8 ) is believed to be too slow to provide agronomic benefits. Using limestone (Ca CO 3 ) and/or dolomite (CaMg( CO 3 ) 2 ) as the additives, crystalline structure breakdown of potassium feldspar is achieved by high‐temperature treatment and a K‐containing multi‐nutrient silicate fertilizer is thus produced. Effect of sintering temperature on the available nutrient contents, mineral phases, and microstructure was investigated. The evolution of K‐containing minerals and their relative dissolution rate were discussed. The dissolution behaviors of other calcium/magnesium silicates were also analyzed. After sintered at 1220°C, the plant‐available Si, Ca, K, and Mg contents in the fertilizer were 15.1%, 21.6%, 5.4%, and 2.4%, with the proportion of 45% potassium feldspar, 33% limestone, and 22% dolomite. Kalsilite ( KA lSiO 4 ) was proved to be the most effective one among potassium feldspar ( KA lSi 3 O 8 ), leucite ( KA lSi 2 O 6 ), and kalsilite ( KA lSiO 4 ), which was totally soluble after 30 minutes extraction in 0.5 mol/L HC l acid. Pseudwollastonite (Ca 3 Si 3 O 9 ) was totally soluble while gehlenite (Ca 2 Al 2 SiO 7 ) and akermanite (Ca 2 MgSi 2 O 7 ) could only be dissolved after extraction of several times. Chemical reaction processes between KA lSi 3 O 8 and CaO/MgO were discussed, and dicalcium silicate (Ca 2 SiO 4 , C 2 S) should be avoided in the reaction system.