Raw diatomite (RD) and diatomite concentrate (DC) were used for the adsorption of cationic Red X-GRL from aqueous solutions. Mono-factor experiments were carried out to investigate the effects of the operation factor, and adsorption kinetics, isotherms, thermodynamics and mechanisms were explored. Similar trend for X-GRL adsorption onto RD and DC was observed. The adsorption capacity of dyes increased slightly with temperature, and the neutral pH was the optimum level. The adsorption processes occurred in accordance with the pseudo second-order model and were well fitted by the Langmuir isotherm model. The main driving forces of the physical adsorption on the diatomite were electrostatic attraction and van der Waals force. The RD could uptake more X-GRL than DC due to its higher content of fine particle and therefore, due to higher surface area available for adsorption. Raw diatomite as a cheap absorbent for X-GRL removal can be suggested as a promising supplement to activated carbon.