尼尔森选矿机广泛应用于金矿选矿领域，查清重矿物富集机制对提高选矿效率具有重要意义。以甘肃某石英脉型金矿石（金品位为6.5×10^-6）为原料，探究了MD3型尼尔森选矿机富集准数（X）与富集机制之间的关系，并考察了不同富集机制下的分选效果。结果表明：当X>9、5<X<9和X<5时，分别对应表面富集、置换富集和淘析富集；当富集锥转速为1 465 r/min、水流量为3.0 L/min时，获得精矿金品位为124.4×10^-6，金回收率为70.36%，选矿效果最好；该条件下粗、中粒金在底层富集环中置换富集，微、细粒金在上层富集环中以表面富集和钻隙沉降的方式富集。当富集准数X值过大时，床层压实，过载现象出现过早；当X值过小时，强烈的反冲水作用导致微、细金流失，二者均不利于金回收，在工业实践中应尽量避免。

The Knelson concentrator，a commonly utilized centrifugal gravity separation device in gold ore processing，is esteemed for its superior recovery efficacy with respect to fine gold.The separation performance of the Knelson concentrator is intricately linked to both material characteristics and operational parameters，with heavy mineral concentration mechanisms varying depending on specific conditions.Consequently，investigating the impact of heavy mineral concentration mechanisms on separation efficiency can be instrumental in enhancing the effectiveness of gold ore separation processes.This study utilized a quartz vein gold ore from Gansu Province as the primary material to investigate the correlation between the concentration criterion （X） of individual enrichment rings of the MD3 Knelson concentrator and the mechanisms of concentration and separation.The findings indicate that heavy minerals were predominantly enriched through plating on the concentrate bed surface when X exceeded 9.In cases where X ranged from 5 to 9，heavy minerals were enriched through the continuous replacement of gangue minerals.Correspondingly，when X was less than 5，heavy minerals were enriched through elutriation.At a rotational speed of 1 465 r/min and a water flow rate of 3.0 L/min，coarse and medium-grained gold were concentrated in the lower rings through substitution，while micro and fine-grained gold were accumulated in the upper rings through surface plating and percolation or migration.The resulting concentrate grade was 124.4×10^-6 with a gold recovery rate of 70.36%，indicating optimal beneficiation effectiveness.Excessive X values led to material bed compaction and premature onset of overload phenomena.If the X value is insufficiently large，the high water flow results in the depletion of micro and fine gold particles，which are detrimental to the gold recovery process and should be minimized in industrial applications.