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Funny, I once made almost the same remark as your "excellent engineer" to a real mining engineer, and he looked at me the same way as yours did you. Mining, he explained, is about getting out ore as nearly uniform in composition as possible, and designing a simple process to separate the tailings from the valuable part, and then applying a maximally simple chemical treatment to the latter, yielding product. A landfill is worst case for mining: everything is maximally diluted, and totally non-uniform. That said, plastic in a landfill is anyway well sequestered. So, I thought there was no point in trying to recycle plastic. But I have been disabused, again: making plastic from petroleum tar releases many times as much carbon into the air as is contained in the plastic, and much more than recycling would. So, if we must have plastic, it is better if it comes from a recycle bin, even if the tar it would otherwise be made from will just end up cracked and burned for bunker fuel. That said, plastic we put in the recycling bin generally just goes straight into the landfill anyway, but costs manual handling by the recycling service in between. So it is hard to draw any sort of lesson about what to do with plastic trash. But anyway glass of all colors can be very efficiently turned into wall insulation and other stuff. The Roman concrete we find in still-intact structures has certain desirable qualities, such as self-healing fractures, and getting stronger with exposure to seawater, but is 1/10 as strong as modern concrete. Their early concrete lacked the better qualities of later formulations. |