Investigation of an eco-sustainable beneficiation technique for the Shankargarh silica sands, Uttar Pradesh (India) and its impact on the soda-lime-silica glass compositions

The Shankargarh silica sand deposits occurring in parts of Prayagraj district, Uttar Pradesh, India, is manually mined and processed to remove deleterious surficial impurities/coatings using pressurized groundwater leading to the groundwater depletion and environmental degradation from the sludge ponds. The present study attempts to suggest an eco-sustainable beneficiation technique for the purification of silica sand samples. The investigation involved the collection of 10 samples from the in situ outcrops and 18 unprocessed samples from the dump sites. The mass magnetic susceptibility (MMS) values (−0.66 to 9.16 × 10 −8 m 3 kg −1 ) and observed hues of brown, yellow, pink and grey, etc. are used to select three representative samples having minimum, intermediate, and maximum MMS. These samples are analysed for their physical and chemical properties, and the sample with maximum impurities (≈ highest MMS) was subjected to various beneficiation processes (magnetic separation, water washing, hot and cold acid leaching, sieving and ultra-sonic cleaning). In all, 9 silica sand (± processed) and a sludge samples are synthesized for their corresponding soda-lime-silica (SLS) glasses. The SLS glasses show limited chemical heterogeneity in terms of their major oxide concentrations. The measured refractive indices of these glasses (1.513–1.531) match well with their respective calculated values (1.498–1.521) as well as earlier reported data for similar SLS compositions. The major outcomes of the present study include the following: (1) some of the silica sand samples (S9, S3-01, S5-02 and S6), collected from the in situ outcrops, can be directly used in the glass and foundry industries without purification; (2) the SLS glasses synthesized during the present study are identical to those reported worldwide; and (3) the magnetic separation, instead of conventional water washing, is suggested as the environmentally sustainable beneficiation technique although hot acid washing maximizes the removal of impurities.