Estimating land transformation area caused by nickel mining considering regional variation

The area of land transformed by the mining of mineral resources greatly varies depending on the type of mineral deposit and mining methods used. Existing factors for the land area transformed per unit of ore mined (land transformation factor) only consider differences in mining methods. In this study, key parameters impacting the area of land transformed were determined and taken into account for nickel with the objective of developing a method for efficiently estimating land transformation factors for mines.

The land transformation factor (m²/t) was defined as the land area transformed to produce 1 t of crude nickel ore, nickel metal (grade >99 %), or ferronickel (grade 20 %). Formulae for calculating the land transformation factor that considered parameters, such as the specific gravity of ores and depth of mining, were built by first classifying mines into three types: laterite ore surface mines, sulfide ore surface mines, and sulfide ore underground mines. Uncertainty analysis for the land transformation factor for each type of mine was conducted, and the key parameters affecting results were identified. Finally, the land transformation factors for 38 mines were calculated using the proposed method.

Land transformation factors for the three types of mines showed that for both surface and underground mines, the values were smaller than the values reported in previous research that were calculated using mining area and production data for a single year. This difference was due to our use of a method assuming the area at the point of maximum extraction depth and maximum overburden dump height. For surface mining, the stripping ratio and ore grade were determined to be key parameters that combined to contribute approximately 80 % of the uncertainty for the land transformation factors of nickel metal. For underground mining, the ore grade and backfilling ratio were determined as the key parameters. The assessment results for mines showed that for surface mining methods, differences in the ore grade and stripping ratio could result in the land transformation factor differing by a maximum of a factor of 10 between mines. These results suggested that the proposed method could efficiently determine the difference between mines.

The proposed method, taking into account key parameters for each mine type, provided a good base for estimating land transformation factors for nickel mining for countries or regions.