237Np isotope is one of the long-lived and hazardous components of the accumulated liquid radioactive waste (LRW). The potential for environmental contamination when the LRW is directly disposed of in deep geological stratum is a matter of concern. Np(V) is highly mobile in the groundwater, and numerous studies are focused on its interaction with natural geological systems and prospective engineered barriers for the radioactive waste repositories. In this work, we studied the neptunium behavior in simulated conditions of acidic liquid radioactive waste injection to the deep permeable stratum collector. To determine components of the host rock preferentially binding the neptunium, and to estimate the effect of elevated temperature on its mobility, a series of laboratory experiments on sorption and leaching of neptunium was carried out using synthetic acid LRW solution and real stratum-collector sand along with individual component simulants. It was found that neptunium sorption on stratum collector sands in the conditions of acidic waste injection is quite low. Clay minerals turned out to be the sorption-dominating components of the host rock for neptunium. Increase in temperature significantly enhances the retention of neptunium on solid phase. Solid-bound neptunium species are sufficiently stable over the two-year experimental time under ambient conditions.