=+solutions. These factors were pH (2 versus 4), temperature (25°C and 85°C), neutralizing agents

[15% (W/W) MgO and 25% (W/W) CaCO3], Fe/

Ni ratio (6 versus 18), and stirring speed (200 and 500 rpm) (“The Effect of Iron Precipitation Upon Nickel Losses from Synthetic Atmospheric Nickel Laterite Leach Solutions: Statistical Analysis and Modelling,” Hydrometallurgy, 2011: 140–152).

Here is data from the resulting fractional factorial experiment:

pH Temp Agents Ratio Speed Iron Removal (%)

2 2 2 1 1 29.19 1 2 2 2 1 84.72 2 1 2 2 2 95.25 1 1 2 1 2 96.08 2 2 1 1 2 49.89 1 2 1 2 2 87.92 2 1 1 2 1 89.22 1 1 1 1 1 96.17