## 1 Introduction  
Rare earth resources in China are abundant and complete in their variety. Among them, the ion-absorbed rare earth that is rich in medium and heavy rare earth elements is widely explored in Jiangxi Province, China [1]. At present, the leaching methods that extract ion-absorbed rare earth elements from mines mainly include in situ leaching and heap leaching [2, 3]. In, in situ leaching, it is difficult to fully explore or predict the discontinuities and inhomogeneities of the mineral deposits. It often leads to the unforeseen loss of leaching liquid, resulting in serious environmental pollution and resource waste [4]. Compared to in situ leaching, heap leaching is a more controllable method, and can effectively reduce the environmental pollution and resource waste. In addition, heap leaching is more efficient in the extraction rate for different grades of rare earth [5]. However, in the traditional heap leaching, the leaching liquid is injected into the rare earth pile from its top. This poses a huge challenge for quickly carrying out vegetation restoration on the top of the pile as the top is covered with leaching liquid for a long time [6]. Therefore, in order to realize the efficient and green development of ion-absorbed rare earth resources, it is necessary to develop an integrated technology of rare earth leaching and vegetation restoration. In this regard, we proposed a novel heap leaching technology that is suitable for vegetation restoration [7], as shown in Figure 1. In the novel heap leaching technology, a heap leaching site needs to be built against a natural mountain, in which a vertical impermeable bedrock is required at the starting end of the heap. A vertical concrete wall can be manually built to replace the vertical bedrock in the absence of one. In addition, the heap leaching site should be relatively flat. The rare earth ore is stacked horizontally level by level, and the leaching liquid is laterally injected into the pile from the side end. After the leaching of the current level pile is completed, the stacking and leaching of the next level pile begins. Meanwhile, the vegetation restoration can be carried out synchronously on the top of the current level pile, where it is not covered by the leaching liquid. The novel heap leaching technology that is characterized by the lateral liquid injection leaves space for the vegetation restoration on the top of the pile. In this way, rare earth leaching and vegetation restoration can be synchronized so as to reduce the environmental damage that is caused by the rare earth leaching. For the traditional heap leaching technology and the novel heap leaching technology, the seepage of the leaching liquid in the piles can be numerically simulated by the software COMSOL, as shown in Figure 2. With regard to the traditional heap leaching, the leaching area on the cross section can reach 91.3% of the total area. The ratio is 88.5% for the novel heap leaching technology. Although the leaching efficiency of the novel heap leaching technology is slightly lower, it is more environmentally friendly. It not only meets the vegetation restoration requirements on the top of the pile, but also reduces resources waste of rare earth elements through controlling the permeability. Therefore, the novel heap leaching technology provides a promising approach to solve the major issues that hinder the healthy development of the rare earth industry such as high environmental pollution and low leaching efficiency [8; 9]. Figure 1: Pile structure of the novel heap leaching technology suitable for vegetation restoration. It is well known that during the heap leaching of rare earth, the leaching efficiency and pile stability are highly dependent on the seepage characteristics of leaching liquid in the rare earth pile. For the zones with lower permeability, it is easy to control the leaching liquid so that it stays in front of these zones, resulting in the insufficient leaching of these zones [10].