The present study employed sodium hexametaphosphate (SHMP) as a depressant for quartz to achieve selective flotation separation of lepidolite. Micro-flotation and artificial mixed-mineral tests confirmed that the introduction of SHMP successfully facilitated the separation of lepidolite and quartz under weak acid conditions. The MD simulations revealed that hydroxylation of non-bridging oxygen atoms on the quartz surface influenced the adsorption of dodecylamine (DDA), while it had no impact on the adsorption of sodium hexametaphosphate (SHMP). Additionally, SHMP was found to form hydrogen bonds with hydroxyl groups present on the quartz surface, thereby enhancing its adsorption capacity and indirectly promoting a higher degree of surface hydroxylation to impede DDA adsorption, thus preserving the hydrophilic nature of the quartz surface. Conversely, the dissolution of K+ in the [Si_6-nAlnO₆] (n=0, 1, 2) rings on the lepidolite surface in an aqueous environment leads to a negative charge on lepidolite. This negatively charged state presents obstacles for SHMP adsorption onto the lepidolite surface; however, it facilitates strong attraction and firm adsorption of positively charged DDA within the ring cavities of lepidolite, resembling an "anchor". The adsorption test revealed that, following treatment with SHMP, a substantial amount of DDA remained adsorbed onto the lepidolite, while only a negligible quantity was observed on the quartz surface. Consequently, the introduction of SHMP enables effective inhibition of quartz under conditions characterized by low hydroxylation levels on its surface (weak acid or neutral), thereby facilitating the production of high-quality lepidolite products.