| Summary: | ABSTRACT The present study assessed the competing behavior between metals and extractants applied to the solvent extraction of calcium and/or nickel present in sulfuric solutions using the extractants Cyanex 272 (bis-2,4,4-trimethylpentyl phosphinic acid) and/or D2EHPA (di-2-ethylhexyl phosphoric acid). Tests were designed to allow equivalent competing conditions between metals and extractants. Considering metal competition in the aqueous phase, calcium extraction remained unaffected in the presence of nickel, while nickel extraction curves with pH displaced to the right in the presence of calcium when D2EHPA (ΔpH1/2 = 1.4) or Cyanex 272 + D2EHPA (ΔpH1/2 = 0.9) were used. Considering extractant competition in the organic phase, metal extractions with Cyanex 272 + D2EHPA closely followed the curves obtained with D2EHPA, thus evidencing that it acts as the main extractant agent, synergism or antagonism effects being attributed to the presence of Cyanex 272. A synergistic increase in the calcium extraction occurred at pH ≥ 4.5, being unaffected in the presence of nickel, whereas rejection for nickel occurred in the whole pH range in the absence of calcium, and at pH < 5.5 in the presence of calcium. For the operating conditions investigated, Ca/Ni separation reached a maximum at pH = 4.5 (calcium extraction > 80%, nickel extraction < 0.25%, βCa/Ni = 2159).
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