Lignin is a common soil organic matter that is present in soils, but its effect on the transformation of ferrihydrite (Fh) remains unclear. Organic matter is generally assumed to inhibit Fh transformation. However, lignin can reduce Fh to Fe(II), in which Fe(II)-catalyzed Fh transformation occurs. Herein, the effects of lignin on Fh transformation were investigated at 75°C as a function of the lignin/Fh mass ratio (0-0.2), pH (4-8) and aging time (0-96 hr). The results of Fh-lignin samples (mass ratios = 0.1) aged at different pH values showed that for Fh-lignin the time of Fh transformation into secondary crystalline minerals was significantly shortened at pH 6 when compared with pure Fh, and the Fe(II)-accelerated transformation of Fh was strongly dependent on pH. Under pH 6, at low lignin/Fh mass ratios (0.05-0.1), the time of secondary mineral formation decreased with increasing lignin content. For high lignosulfonate-content material (lignin:Fh = 0.2), Fh did not transform into secondary minerals, indicating that lignin content plays a major role in Fh transformation. In addition, lignin affected the pathway of Fh transformation by inhibiting goethite formation and facilitating hematite formation. The effect of coprecipitation of lignin on Fh transformation should be useful in understanding the complex iron and carbon cycles in a soil environment.

木质素是土壤中常见的土壤有机质，但其对水铁矿（Fh）转化的影响仍不清楚。通常认为有机物会抑制 Fh 转化。然而，木质素可以将 Fh 还原为 Fe(II)，其中发生 Fe(II) 催化的 Fh 转化。在此，在 75°C 下研究了木质素对 Fh 转化的影响，作为木质素/Fh 质量比 (0-0.2)、pH (4-8) 和老化时间 (0-96 小时) 的函数。对Fh-木质素样品（质量比=0.1）在不同pH值下的陈化结果表明，与纯Fh相比，Fh-木质素在pH 6时Fh转变为二次结晶矿物的时间明显缩短，并且Fe(II )-Fh 的加速转化强烈依赖于 pH 值。在pH 6下，在低木质素/Fh质量比（0.05-0.1）下，次生矿物形成时间随着木质素含量的增加而缩短。对于高木质素磺酸盐含量的材料（木质素：Fh=0.2），Fh没有转化为次生矿物，表明木质素含量在Fh转化中起主要作用。此外，木质素通过抑制针铁矿形成和促进赤铁矿形成来影响Fh转化途径。木质素共沉淀对 Fh 转化的影响有助于理解土壤环境中复杂的铁和碳循环。