In this article, we study exponents which preserve complete monotonicity of functions on lattices. We prove that for any completely monotone function $f$ on a finite lattice, $f^α$ is completely monotone for all $α\geq c$, where $c$ is explicitly described. For finite distributive lattices we show that the bound $c$ is sharp. Important examples of completely monotone functions are void functionals of random closed sets. We prove that if $V_{\mathcal{X}}$ is the void functional of a random subset $\mathcal{X}$ of $[n]$, then $V_{\mathcal{X}}^α$ is void functional of some random closed set for $α\geq n-1$. The results are analogous to the result of FitzGerald and Horn on Hadamard powers of positive semi-definite matrices. Also, we study the question of approximating an $m$-divisible random set by infinitely divisible random sets, and its generalization to lattices.