 Let's talk about how to convert metal sulfides or metal carbonates to metal oxides. In a previous video, we talked about how to get pure metals from metal ores. And we said that these are the four steps for doing it. And we also talked about the first step, which was enrichment of the ore. Basically, we take a metal ore and we crush it into pieces. And then we separate the metal compound from its impurities. And if the metal compound is not metal oxide, it's a metal sulfide or metal carbonate. Then first of all, we will convert them to metal oxide form. And that is because it is easier to separate metal from its oxide. And that will happen in the third step, reduction to metal. And after that, we will refine this metal to get pure metal in the fourth step. But in this video, let's talk about the second step. Now, let's say, for example, we are dealing with zinc ore. We have the zinc ore over here. And in the first step, enrichment of the ore, we crushed it into pieces and we separated the zinc compound from the impurities. Now, this zinc compound, this happens to be zinc sulfide. And now, since this compound is not an oxide, we will first have to convert this to a metal oxide. Then we will react this, we will heat this with excess of oxygen. And that's how zinc sulfide will convert to zinc oxide. Whereas if we had zinc carbonate, then we will heat this in limited supply of oxygen. And that's how a carbonate converts to oxide. So the thing to remember here is that the compound that we got after enrichment of ore, if that is a sulfide, then we need to heat it in the presence of oxygen. And that's how it will get converted to oxide. And this makes total sense. If we need to remove sulfur and add oxygen, we will have to react this with oxygen, right? Now, this process is called roasting. Just like how we roast chicken or vegetables in the presence of oxygen, that's how the sulfide ores are roasted in the presence of oxygen. Now, the second thing was, if this metal compound is a carbonate, then in that case, we need to heat it in limited supply of oxygen. And that's how we will convert a carbonate to oxide. And this also makes sense. See, carbonate already has an oxygen, so we don't need to provide a lot more oxygen over here. And this process where we heat carbonate in limited supply of oxygen is called calcination. And this goes without saying that if the metal compound is already an oxide, for example, if you had an iron ore and you directly got iron oxide, in that case, you do not need to convert it to metal oxide. It's already in its oxide form, right? And in case you're dealing with inert metals like gold and platinum, then in that case, after doing the enrichment of ore, you would not get metal compound. You would not get a compound of gold because it does not form any compound. You will get gold in its free state. And for that, you do not need to convert it to metal oxide and then later reduce it to get the metal. You already have the metal with you, right? So you can directly take the inert metal that you get here to the refining step, okay? So in the second step, we converted the metal compounds that were there in the form of sulfides or carbonates into oxides. And for this, we used roasting or calcination process. Now in future videos, we will see how we can remove the oxygen out of these metal oxides and reduce them to get metal out of them. And after we have got the metal, we will see how to refine those metals to get pure metal. 99.99% pure metal.