can i still keep the carbon

I'd throw it away and get a new bag of carbon. Carbon is only good for awhile. It'd absorb whatever it can. It can also release whatever it absorbed back in the water as well depending on it's affinity for other chemicals.

I believe you can "recharge" them somehow, but IMO it's a waste of time and it's not even for sure that it works.

I'm puzzled here. I was always told that carbon adsorbs rather than absords. Which very simply means it takes in but doest release back out. I would still throw away the carbon myself, but it can release any of what its collected back to your tank, the concern with it is that I would want to be sure it had adsorbtion capabilities left the next time I wanted to use it. I NEVER run carbon in any of my tanks as IMO its not needed and just another way the hobby bleeds money out of newbies to it. I keep activated carbon on hand at all times to remove medcations from the water should I need to change meds mid treatment, or incase any toxins accidentally find their way into the tank. Thats it. I add liquid fertilisers for some plants and tabs fdor others since my tanks are planted and all the carbon would do is adsorb the base elements in these fertilisers than my plants want and need. Its your call whther you continue to use carbon, but carbon is one of these debates in this hobby that will never find a conclusion like salt. Some swear by it, and others like me swear at it. But for now, I would bin the stuff thats been used as its only got a finite life and then its inert anyway.

Quagaar is correct. Carbon does not release what it has taken up, but after a while it ceases to remove anything from the water. It becomes biologically active though--the beneficial bacteria colonize the carbon quite readily. So, since it's been in your tank for so long, it's likely no longer chemically active, but is biologically active.

I don't run carbon on my tanks unless I'm removing medication or tannins.

Carbon can be reactived, but it needs super high temps that you just can't get with household equipment. Activated carbon can also release stuff it has trapped if it comes in contact with something that will form a more powerful bond, and often this is medication. Thus meds will bond with the carbon (like you want it to do) and throw out the other nasty bits it has taken in.

I agree that you need to throw it out. I also agree that it is generally a waste of time to use in a tank as sponges and filter floss or bioballs are a much better choice.

Activated carbon also has a high affinity for bonding with water as well, which means that after a week at the most it won't be grabbing anything toxic out of your tank. So if you want to keep carbon in your tank you need to change it constanly for it to do any good.