A process for extracting Cs-137 from i) an acidic solution obtained by dissolving an irradiated solid target comprising uranium, ii) an acidic solution comprising uranium which has previously been irradiated in a nuclear reactor, or iii) an acidic solution comprising uranium which has been used as reactor fuel in a homogeneous reactor, the acidic solution i), ii) or iii) having been treated to harvest Mo-99, wherein the process comprises contacting the treated acidic solution with an adsorbent comprising ammonium molybdophosphate (AMP). In an embodiment, the AMP is combined with an organic or inorganic polymeric support, for example AMP synthesized within hollow aluminosilicate microspheres (AMP-C).