Chairoj Rattanakawin and Aung Lay Tin

DOI: 10.14456/sjst-psu.2019.79

pp. 664 - 668

Abstract

The purpose of this research was to study the feldspar of Nopphitam District, Nakhon Si Thammarat Province,
Thailand with emphasis on Hardgrove grindability and determination of the approximate work index. Feldspar samples were
collected, prepared, and analyzed for their chemical composition. From the analysis of the alkaline metal oxides, all samples were
characterized as sodium feldspar. The Hardgrove grindability test used a ball-race test mill. The Hardgrove grindability indices of
these feldspar samples had an average of 46.25. Knowing the average Hardgrove index, a calculated work index of 12.88
kW/STPH was estimated using Aplan’s empirical formula. This average work index was less comparable to those of feldspar
ores given in the literature. Therefore, the method of Berry and Bruce was used to determine the specific energy and approximate
work index. By running a batch dry-grinding test in a rod mill, an average specific energy of 7.34 kW/STPH was determined
using Bond’s formula with the reference work index of 11.25 kW/STPH. This specific value is limited to these test conditions:
(1) 18x36 cm mill with material hold-up of about 0.08, media loading of about 0.4, and half interstitial filling and (2) each
sample must be ground by 8 steel rods with dimensions of 3.5x35 cm each for 15 min. Under these conditions, the approximate
work indices of various minerals can be rapidly estimated knowing the 80% passing size (μm) of both feed and product from rodmilling that conforms to the indicated conditions. For example, the approximate work index of Sam Ngao sodium feldspar was
11.03 kW/STPH. This work index was quite comparable to those acquired from various mill manufactures. To obtain more
accurate values of sodium feldspar’s work indices, the time-consuming Bond procedure should be performed with a number of
corrections for different milling conditions.