But before the brine can be processed, it has a small amount of hardness to it because of the presence of calcium sulfate. If this is left, it will build up and clog pipes and reduce the life of the electrolytic cells. The calcium sulfate must be removed before it goes into the cells to be electrically charged. Pretty innocuous stuff, but nevertheless it is a waste. Anybody who makes chlorine has the same waste.
Calcium carbonate is the same white buildup that can be seen on dry coffee pots.
It is also a pure form of limestone. Which is why it makes an ideal replacement for the rail cars of limestone rock that the company was bringing to the plant to neutralize the hydrochloric acid. It was better than the limestone, said Pat Schreckenbach, project engineer who coordinated the construction of the project. So periodically, they have to take all of that flint out. Because limestone has impurities that are sometimes left behind after the reaction, sometimes the reaction unit has to be shut down to remove the flint and other impurities that are left behind.