Why would they do so, when the coins are worth slightly more than the silver in them? You not only lose that small value, but there’s the cost of refining, casting, etc. There’s no reason to do so, and several reasons not to. The site I linked to is evidence that bags of junk silver are very common.
Supply and demand. We buy about $1000. face value in silver coins/day these days. We sell back, over the counter, about $200. face value/day. I would assume that’s typical of many coin dealers. The supply coming in overwhelms the demand for the item. Thus, it goes to the refinery, to be melted into pure silver bars, for which there is a great demand worldwide.
Sure it can, if the rest of the world chooses to value gold at a higher price than your gold coin’s stated monetary value.
The US, prior to April,1933, said that a $5 gold coin had $5.15 worth of gold value. If you gave your bank a $5 banknote, the bank would give you a $5 gold coin. By late 1933, with the US no longer on the Gold Standard, the world price of gold had risen to $35/ounce. So, if you were a Foreign government such as France, you could have redeemed $5 in US banknotes(spent by tourists) for a $5 gold coin, which you could have sold on the open market for $8+. Pretty good profit.
Ah, thanks for the correction. I should have checked Wikipedia before posting. According to Wikipedia, nickels are currently worth 7.3 cents and pre-1982 pennies are worth almost 3 cents.