Extraction of pectin (Pec) from banana (Musa paradisiaca L.) peels, the agricultural waste of banana fruit treated in acidic condition, and its fabrication into pectin–activated carbon (Pec–AC) composite by impregnation method were investigated. This Pec–AC composite was applied as an adsorbent to simultaneously remove multi-lanthanides, namely yttrium (Y), lanthanum (La), cerium (Ce), neodymium (Nd), and samarium (Sm), which were released from an acidic silica sand aqueous solution. Various fractions of Pec in Pec–AC composite and the effects of different parameters on the adsorption capacity of the multi-lanthanides were also evaluated. At the optimum condition, the adsorption capacity of the lanthanides was 84.4, 77.7, 67.5, 57.5, and 53.7% for Y, Nd, Sm, Ce, and La, with respect to their content in the silica sand. The Qmax value was estimated to be 21.80, 27.78, 18.22, 21.09, and 24.91 mg g−1 for La3+, Y3+, Nd3+, Sm3+, and Ce3+, respectively. Fourier-transform infrared analysis suggests that the lanthanides are bound to the electronegative functional groups on the active sites of the Pec–AC composite. The simultaneous adsorption of the lanthanides on Pec–AC composite is governed by the pseudo-second-order kinetics, and the adsorption process of the lanthanides can be described by Temkin isotherm model. Overall results suggest in this study that the Pec–AC composite is an efficient potential adsorbent to simultaneously absorb multi-lanthanides from leachate of silica sand as the primary step of isolation of lanthanides.