The release of liquid effluents containing heavy metals, notably Cr (VI), into the environment is a significant contributor to water pollution. Consequently, there is a growing concern about treating these effluents before their discharge. In this context, our study introduces an innovative approach to produce a novel chloride-doped polypyrrole/Diatomite (Cl-PPy/DT) nanocomposite through in situ polymerization. We examined the physicochemical properties of Cl-PPy/DT using various analytical techniques, including structural, textural, morphological, and thermal analyses, confirming the successful formation of the composite. For Cr (VI) removal via batch adsorption, the efficiency of Cl-PPy/DT surpassed that of Cl-PPy and diatomite by 2.21 and 3.75 times, respectively, at a Cr(VI) concentration of 25 ppm. This suggests a robust synergistic effect between diatomite and Cl-PPy, where both components resist aggregation, resulting in a loose structure and optimal exposure of active sites. Using response surface methodology, we refined adsorption parameters such as contact time, initial metal concentration, and adsorbent quantity. Results indicated that adsorption followed a quadratic polynomial model with high regression parameters (R2 value = 99.6%). Kinetic findings demonstrated that Cr(VI) adsorption on Cl-PPy/DT aligned with the pseudo-second-order model. Moreover, at 25 °C, the Langmuir model effectively correlated with equilibrium data, revealing a maximum adsorption capacity (qmax) of 89.97 mg/g for the Cl-PPy/DT adsorbent. Notably, the adsorbent exhibited renewability and reusability for up to four cycles, indicating its potential for large-scale use as a competitive adsorbent. Display omitted •New stable diatomite-polypyrrole composite was successfully synthesized and applied for Cr(VI) removal.•PPY@Diatomite provides a High adsorption ability for Cr (VI) in aqueous solutions.•Response surface methodology was applied to optimize the Cr (VI) adsorption behavior.•PPY@Diatomite was a promising and reusable material for Cr(VI) removal.