Do yourself a favor and forget the kitty litter idea. I have beat this subject to death and there are more kitty litter horror stories than there are success stories.
Laterite is not similar to Flourite. Flourite is a complete substrate and Laterite is a substrate additive. They are both a source of iron but they are by no means similar. If Flourite is too expensive or unavailable then Laterite is a good way to go.