I save my bacon grease when cooking bacon and use it in several recipes. When i render it and store in the refrig some becomes a white solid and some remains in a gelatin state. Why?
If the white solid is on top, and the gelatin below, it's just an issue that it's not all fat -- you have meat juices in there, too, which can turn to jelly.
If you're trying to store it for a longer-term, you'll want to strain it, then let it cool. Lift off the solid white portion, scrape any jelly stuck to the bottom, then heat back up the oil.
Bring it back up to the water boiling point, and it might start to bubble. If it gets above 100°C, you're fine. Otherwise, wait 'til the bubbles go away and it gets above 100°C, then hold it for a few minutes. Let that cool some, then put it into a clean container and put it back in the fridge to cool completely.