difficult-to-float的用法和樣例：
例句
- It is difficult to concentrate for Arsenical gold Mineral.
含砷金礦屬難選礦石。 - Primary gold ore from Bangi, Guizhou, belongs to a clastic-type, finely disseminated, refractory particles.It is difficult to extract gold from the ore by cyanide infusing.
貴州板其原生金礦石屬碎屑岩類微細浸染型難選冶礦石，在氰化浸出之前需進行預處理。
