yeah reusing limonene works perfectly.. I have no idea how many times you can reuse while still being effective, but I have reused several times in extractions and noticed no diminish in the alkaloid dissolution properties.
If you want, as soulfood said, you can wash limonene with an acidic solution and then basic solution. I wouldnt do it with a strong hcl solution though as I've seen people posting in the forum that limonene seems to react with strong hcl solutions, but I dont say this from experience. But a vinegar wash and then a basic wash, whether its NaOH or sodium carb or whatever, should be more than enough. I have re-used limonene without doing any wash at all (appart from the salting to get the alks out) and it was still working perfectly.