Abstract: The invention provides a method for the preparation of a pitch spinnable into pitch filaments as a precursor of carbon fibers starting from a pitch material such as coal tar and coal tar pitch. Different from the conventional procedure involving hydrogenation of the starting pitch, the starting pitch in the inventive method is first heated together with an aromatic oil, preferably, in the presence of a cracking catalyst such as silica-alumina and zeolite at 350.degree. to 500.degree. C. for 10 to 60 minutes under no pressurization with hydrogen and, after removal of insoluble materials, then heated at a temperature of 430.degree. to 600.degree. C. The thus obtained pitch for spinning has good spinnability and the carbon fibers prepared from the pitch have a unique microscopic structure and excellent physical properties exceeding by far the conventional pitch-based carbon fibers and approximating the HP-grade carbon fibers prepared from polyacrylonitrile fibers.

Abstract: The compound thiohumic acid resulting from replacing at least a part of the carboxyl groups in humic acid by thiocarboxyl groups, i.e., ##EQU1## as well as a heavy metal adsorbent containing thiohumic acid as its active ingredient. This new compound is obtained by treating humic acid with a halogenating agent to form humic acid halide and treating such halide with a thiolating agent.