The basic principle and application of gravity

重选法是根据各种矿物密度及粒度的不同，借助于流体动力和各种机械力的作用，造成适宜的松散分展和分离条件，从而得到不同密度或不同粒度产品的工艺过程。矿石采用重选分离的难易程度，习惯上用下式评定：

Gravity method is according to different mineral density and particle size, with in the role of hydrodynamic and mechanical force, causes the exhibition and separation conditions of division of appropriate loose, resulting in the process of different density and different size products. The ore difficult degree of gravity separation, with rating habits:

E=（δ2-ρ）/（δ1-ρ）

E= (2- P) / (1- P)

式中 δ1——矿石中有用矿物的密度；

Delta 1 - the density of useful minerals in ores;

δ2——矿石中脉石矿物的密度；

Delta 2 - density gangue minerals in the ore;

ρ——重选介质的密度。

P: medium density.

根据E值,矿石分选的难易程度可分为极易重选(E>2.5)、容易重选(E=1.5~1.25)、中等可选(E=1.75~1.5)、比较难选（E=1. 5~1.25）和极难重选（E<1.25）等几个等级。由于金矿石中金矿物的密度较脉石矿物大得多，E值较大，所以金矿石宜采用重选法处理。

According to the values of E and the degree of difficulty of the separation of ore can be divided into easy re-election (E>2.5), easily re elected E=1.5~1.25 medium optional E=1.75~1.5, relatively refractory (E=1. 5~1.25 and extremely difficult to gravity (E<1.25), and several other levels. The gold in gold ore mineral density than the gangue minerals much larger, E value is large, so the gold ore should be used in gravity separation process.

重选法是一种古老的选矿方法，并较早地应用于黄金选矿生产中，是一种主要的选金方法。砂金矿基本上都是利用重选法。用重选法从脉金矿中回收金也十分有效。地露天开采的砂金矿而言，还可用立式离心选矿机选金。

Gravity method is an ancient method of dressing, and earlier applied in ore dressing production of gold, is a main gold concentration technique. Placer gold deposits are basically the use of gravity method. By gravity method of recovering gold from gold is also very effective. In the open pit mining of the sand, the vertical type centrifugal concentrator can also be used.