Lignin having chemically bound sulfur and phosphorus groups mainly as

Abstract

A product comprising, a water insoluble lignin material, at neutral or acid pH, having chemically bound a sulfur(S) content from at least 9.5%, and a phosphorus(P) content from 3.3 to 10%. At least 50% by weight of the S and P content is thiophosphate. In said lignin material the mole ratio S/P is at least 1.8 that of S to aromatic unit (S/Ar) is greater than 0.7, and the P/Ar ratio is from 0.3 to 0.8. The lignin material has chelating capacities for gold at pH 2 of at least 2.2 millimoles per gram of lignin material. On IR analysis the lignin material has infra-red absorption bands evidencing P.dbd.S, P--S or Ar--S, P--O--Ar, aromatic, CH.sub.2 --S, and P--O--C groups in the vicinity of 730-750, 640-670, 1080-1110, 1490-1510, 820-845, and 965-995 cm.sup.-1, respectively. In the absence of interferring IR bands, the sum of the intensity of the bands in the vicinity of 640-670 cm.sup.-1 and 730-750 cm.sup.-1 over the intensity of the band in the vicinity of 1080-1110 cm.sup.-1 is greater than 1. The product, substantially free from unbound sulfur, may be used in chelation, floatation processes, as flame retardant, and for agricultural uses. A method of making the above comprises heating a lignin product with at least an exact equivalent molar ratio of phosphorus pentasulfide (P.sub.4 S.sub.10). The reaction product must be specially treated to recover it.