Not Carolyn, but I want to contribute anyway. My notes suggest about 0.02% by weight EDTA powder based on the total batch weight of lotion. Yes, that's a teeny tiny amount.
Disclaimer: I have just recently started to include a chelator in my lotions, so my real-world experience is limited. Hopefully Carolyn will share what she recommends -- she has a lot more experience to back up her recommendations. @IrishLass
is another person who uses a chelator in lotion -- perhaps IL will also share what works for her.
You will want to use DIsodium EDTA for products like lotions that have a neutral to acidic pH (pH at or below 7). TETRAsodium EDTA should be used in soap, because soap is alkaline (pH above 7).
In addition to extending the shelf life of fats in a lotion, the use of a chelator also boots the effectiveness of the preservatives added to lotion to inhibit microbial growth. Certain trace metals are required to support living organisms. If the chelator immobilizes those metals, then microorganisms in the lotion will find it harder to reproduce and thrive.
Just to be clear -- A chelator is NOT a preservative. Use it IN ADDITION TO a broad spectrum preservative, not in place of a preservative.