The content of potassium in the filtrate was measured by the potassium
tetraphenylborate gravimetric method. Tomeasure the content
of potassium in the K-feldspar ore or leach residue, the solid
samples were first digested. Approximately 0.5 g of K-feldspar ore
or leach residue was mixed with 4 g of NaOH and 1 g of Na2O2 in a
nickel crucible, was smelted in a muffle furnace at 750 °C for 10 min,
and was then dissolved in a mixed solution of 30 ml of dilute sulfuric
acid with a volume ratio of 98 wt.% sulfuric acid to deionized water 1:1
and 50 ml of dilute hydrochloric acid with a volume ratio of 31 wt%
hydrochloric acid to deionized water 1:1. The content of potassium in
the leach liquor was also measured by the potassium tetraphenylborate
gravimetric method.
The content of chloride in the filtrate was determined by the silver
chloride gravimetric method.
The XRD analyses of the calcined slag and leach residue were performed
using a Philips X'pert PRO diffractometer employing graphitefiltered
Cu Kα radiation (λ=0.15406 nm) with an accelerating voltage
of 40 kV and tube current of 30 mA. Data points were acquired by step
scanning with a ratio of 12(°)·min−1 from 2θ=10° to 2θ=80°.
The surface morphology of the raw K-feldspar ore and the calcined
slag was observed using a Hitachi S-4800 scanning electron microscope
(SEM) at an accelerating voltage of 5 kV. The relative elemental abundance
of the K-feldspar ore and the calcined slag was analyzed with
an energy-dispersive X-ray spectrometer (EDS, Oxford IE 250).