Nigeria’s lithium-bearing pegmatites could support local mineral processing and battery-material production, but commercial success depends on more than ore availability. A workable operation must address low feed grade, variable spodumene–mica mineralogy, energy demand, reagent recovery, water use and unstable lithium prices. This study develops an integrated process model for a representative Nasarawa-type pegmatite containing 1.08% Li₂O. The proposed route combines staged crushing, de-sliming, two-stage dense-medium separation, flotation of middlings, direct low-temperature NaOH roasting, counter-current water leaching, impurity removal and carbon-dioxide precipitation of lithium carbonate. Water, caustic solution and silicate-rich residues are partly recovered for reuse. Response-surface analysis was used to examine roasting temperature, NaOH-to-spodumene ratio and residence time. The sustainability-adjusted optimum was 333°C, a ratio of 1.47 and 83 minutes, producing a predicted lithium extraction of 97.5%. One tonne of ore yielded about 22.3 kg of lithium carbonate, representing an overall recovery of 83.5%. For a 200,000-tonne-per-year plant, annual output was estimated at 4,460 tonnes. Installed capital was projected at US$98.2 million, operating cost at US$6,460 per tonne, net present value at US$80.7 million, internal rate of return at 22.9% and minimum selling price at about US$10,600 per tonne. Environmental screening suggested that renewable electricity, heat recovery, caustic recycling and residue utilization could reduce climate impacts by nearly half. These results are design estimates and require pilot testing, residue assessment and local cost validation before investment. The model therefore provides a preliminary basis for comparing technical performance, profitability and environmental trade-offs within Nigeria’s responsible, emerging domestic hard-rock lithium industry sector.