First, after the CV-based pre-selection a video interview with self-recorded answers, where you can re-record yourself if you're not satisfied with them. If they like you, they will invite you for a so called assessment day, where in my case you will be "competing" against 4 other candidates. The day includes 2 individual interviews, one case study, one presentation about pretty easy topic choices (fav. book, a leader you admire, a trend that had an impact on the world, a trend that had an impact on cargill) and one trading game which in my opinion was pretty difficult if you haven't done it before. Also, before going to the company, they send you two tests that you have to complete, one verbal and one numerical reasoning test.
In general I think putting all these stages in one day is very demanding, but on the other hand you really get an understanding about the company, your potential colleagues and your tasks. But in my opinion, in order to get in you really have to be engaged in commodity trading, interest is not enough.