采用颚式破碎机或辊式破碎机均难以实现对废旧印刷电路板（PCB）的充分粉碎，从粉碎过程来看，具有剪切和冲击作用的圆盘粉碎机或振动磨样机的粉碎效果要优越一些。PCB的资源组成包括47%的金属、27%的塑料以及26%的玻璃、陶瓷等难熔氧化物。与天然资源相比，Au、Ag、Cu、Pb、Sn等金属含量特别丰富，分别达到了300g/t、5-10Kg/t、19.66%、3.93%和3.68%，此外还含有Fe、Al、Zn、Ca、Mn、Ni、In 等十多种有价金属，具有重要的回收价值。

The galvanic coupling formed in origin-potential flotation systems of sulfide minerals could be divided into three types: sulfide mineral-sulfide mineral-water system; sulfide mineral-steel ball-water system; and sulfide mineral-sulfide mineral-collector system. In this paper, taking lead, zinc, iron sulfide mineral systems as examples, models of galvanic coupling are showed and the effects of galvanic coupling on flotation are discussed. A galvanic contact between galena (or sphalerite) and pyrite benefits to decrease the content of sphalerite in lead concentrates, and can enhance remarkably the absorption of collector on the galena surface. During grinding, due to galvanic interactions between minerals and steel medium, Fe (OH) 3 formed will coat the cathodic mineral surface, affecting its floatability.

Through thermodynamic calculation and electrochemistry analysis, taking the galena as example, the basis for collector matching in origin potential flotation (OPF) was studied. The results of thermodynamic calculation show that the upper limit value of pH and flotation potential of diethyldithiocarbamate (DDTC) is higher than that of xanthogenate (KBX), which indicates that the collecting ability of DDTC for galena is better than KBX. The results of the interface capacitance analysis show that lead diethyldithiocarbamate (PbD2) is more steady than lead xanthogenate (Pb(BX)2) on the galena surface in the oxidation condition; the resistance analysis shows that D2 (DDTC oxidizes into its dimmer) and dixanthogen (BX) 2 would occur non-faradic desorption on the pyrite electrode surface when the potentials are respectively above 0.13V and 0.2V. Then synthetical criterion ΔE of collecting ability and selectivity was proposed. The results forecasted by this criterion were confirmed through flotation experiments of ore.

The electrochemical oxidation of galena in collectorless and collector flotation systems, particularly in strong alkaline media, were studied. The results show that, as pH values high than 12.5 and potentials below 0.17V, the oxidation products of galena are elemental sulfur and HPbO2-. Elemental sulfur was present on the mineral surface in excess of oxidized lead species due to dissolution of HPbO2-, which is beneficial to the flotation of galena. Under the same conditions, sphalerite and pyrite were depressed as a result of significant surface oxidation. Diethyldithiocarbamate (DDTC) was found to be the most suitable collector for galena flotation in strongly alkaline media. The very potential producing hydrophobic PbD2-the surface reaction product of DDTC with galena, is 0 to 0.2V. Meantime DDTC can depress the surface over-oxidation of galena. Investigations also indicate that, in the range of-0.9V to 0.6V, hydrophobic PbD2 can be firmly adsorbed on galena.

In the light of the knowledge gained by the study of electrochemical flotation for galena and selective flotation of galena from lead-zinc-iron sulfide ores, a technology for accurate potential control based on intrinsic electrochemical behavior in grinding-flotation systems has been developed and is called "Original Potential Flotation (OPF)". The optimum conditions for the Original Potential flotation of galena from the Pb-Zn-Fe sulfide ores were: pH values of 12.5-12.8, potential of 150-180mV and with diethyldithioncarbamate (DDTC) as collector. Lime was used as a regulator of pH, meanwhile, it could stabilize special potential very well, and this special potential was exactly flotation potential of galena. This technology had been applied successfully in potential-control flotation of galena in many complex lead-zinc-iron sulfide mines in China.