Sodium aluminate solution after desilication enters the settling tank of silica slag through the distributor. The settling silica slag is pumped out in the bottom flow tank and sent to the silica slag filter by the bottom flow pump. The overflow of the settling tank goes to the original liquid tank (overflow tank) and is pumped into the vane filter. The silicon slag filtered by the leaf is washed into the silicon slag trough with solution first, then pumped to the silicon slag filter. The semen filtered by the leaf enters the semen trough and is pumped to the decomposition trough for decomposition. The filtrate of the silicon slag filter returns to the original liquor tank of the silicon slag settling tank and the overflow of the settling tank enters the leaf filter together. The silicon slag filtered by the silicon slag filter is sent to the raw material section to be proportioned. Among them, the slurry after desilication is sent into the settling tank of silicon slag before entering the leaf filter for settling, in order to reduce the load of the leaf filter, so that most of the silicon slag is separated from the solution in the settling tank, and only the overflowing solution is sent to the leaf filter for leaf filtration. This can reduce the load of the leaf filter, thereby reducing the number of leaf filter.