I just did the penny to gold demo which uses zinc powder and sodium hydroxide. I used 200ml 3M NaOH, and 10g of Zinc (did it twice with 100ml and 5g each time). Now that its over, I have a whitish grey solid leftover which I am assuming is sodium zincate Na2[Zn(OH)4]. I can't seem to find any information about sodium zincate and was wondering how to dispose of it. I have about 17g of this substance total. I'm concerned because during this experiment a chunk of wet zinc powder fell onto some paper and burnt a small cigarette sized hole in it. Thanks.